Light source

ABSTRACT

A light source has a rear glass substrate and a front glass substrate having a plate surface disposed in facing relation to a principal surface of the rear glass substrate. The plate surface of the front glass substrate is coated with a phosphor. A two-dimensional array of electron emitters is disposed on the principal surface of the rear glass substrate. A space defined between the rear glass substrate and the front glass substrate is filled with a gas. The gas may be an Hg (mercury) gas or an Xe (xenon) gas.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light source (including a planarlight source) comprising electron emitters each having an upperelectrode and a lower electrode that are disposed in an emitter.

2. Description of the Related Art

Recently, electron emitters having a drive electrode and a commonelectrode have been finding use in various applications such as fieldemission displays (FEDs) and backlight units. In an FED, a plurality ofelectron emitters are arranged in a two-dimensional array, and aplurality of phosphors are positioned in association with the respectiveelectron emitters with a predetermined gap left therebetween.

Conventional electron emitters are disclosed in Japanese Laid-OpenPatent Publication No. 1-311533, Japanese Laid-Open Patent PublicationNo. 7-147131, Japanese Laid-Open Patent Publication No. 2000-285801,Japanese Patent Publication No. 46-20944, and Japanese PatentPublication No. 44-26125, for example. All of these disclosed electronemitters are disadvantageous in that since no dielectric body isemployed in the emitter, a forming process or a micromachining processis required between facing electrodes, a high voltage needs to beapplied to emit electrons, and a panel fabrication process is complexand entails a high panel fabrication cost.

It has been considered to make an emitter of a dielectric material.However, various theories about the emission of electrons from adielectric material have been presented in the documents: Yasuoka andIshii, “Pulsed Electron Source Using a Ferroelectric Cathode”, OYOBUTURI (A monthly publication of The Japan Society of Applied Physics),Vol. 68, No. 5, pp. 546-550 (1999), and Puchkarev, Victor F. andMesyats, Gennady A., “On the Mechanism of Emission from theFerroelectric Ceramic Cathode”, Journal of Applied Physics, Vol. 78, No.9, 1 November 1995, pp. 5633-5637.

In the conventional electron emitters described above, electrons thatare restrained on the surface of a dielectric body, the interfacebetween the dielectric body and an upper electrode, and the defectivelevel in the dielectric body are discharged by an inversion of thepolarization of the dielectric body. That is, if the polarization of thedielectric body is inverted, then the amount of emitted electrons issubstantially constant, not dependent on the voltage level of an appliedvoltage pulse.

However, the conventional electron emitters are problematic in that theelectron emission is not stable and can only be performed several tensof thousands times at most, and the electron emitters are not practicalwhen used as light sources, for example.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a light source whichcomprises electron emitters each having an emitter made of a dielectricbody, the electron emitters being prevented from emitting excessiveelectrons to prevent electrodes or the like from being damaged by theemission of electrons, thus allowing the light source to have a longservice life and increased reliability.

Another object of the present invention is to provide a light sourcewhich is capable of easily producing a high electric field concentrationand providing many electron emission spots for emitting electrons with alarge output and a high efficiency.

According to a first aspect of the present invention, there is provideda light source of the discharge lamp type, wherein electrons ignite orassist in an electric discharge, a source of the electrons comprises anelectron emitter, and the electron emitter comprises an emitter of adielectric material and a first electrode and a second electrode whichare disposed on the emitter, wherein when a drive voltage is appliedbetween the first electrode and the second electrode, at least a portionof the emitter has its polarization inverted or changed to emitelectrons.

According to a second aspect of the present invention, there is alsoprovided a light source for emitting light by exciting a phosphor withan ultraviolet radiation generated from a gas sealed in a space in thelight source, wherein electrons assist in generating the ultravioletradiation from the gas, a source of the electrons comprises an electronemitter, and the electron emitter comprises an emitter of a dielectricmaterial and a first electrode and a second electrode which are disposedon the emitter, wherein when a drive voltage is applied between thefirst electrode and the second electrode, at least a portion of theemitter has its polarization inverted or changed to emit electrons.

According to a third aspect of the present invention, there is alsoprovided a light source for emitting light from a phosphor by havingelectrons and/or ions impinge upon the phosphor, the electrons and/orions being produced when electrons impinge upon molecules of a gassealed in a space in the light source and ionize the molecules of thegas, wherein a source of the electrons comprises an electron emitter,and the electron emitter comprises an emitter of a dielectric materialand a first electrode and a second electrode which are disposed on theemitter, wherein when a drive voltage is applied between the firstelectrode and the second electrode, at least a portion of the emitterhas its polarization inverted or changed to emit electrons.

The emitter may be made of a piezoelectric material, ananti-ferroelectric material, or an electrostrictive material.

Operation of the electron emitter according to the first through thirdaspects of the present invention will be described below. When the drivevoltage is applied between the first electrode and the second electrode,at least a portion of the emitter has its polarization inverted orchanged, emitting electrons from an area near the first electrode whosepotential is lower than the second electrode. Specifically, as thepolarization is inverted or changed, a local electric fieldconcentration occurs on the first electrode and positive poles ofdipoles near the first electrode, drawing primary electrons from thefirst electrode. The primary electrons drawn from the first electrodeimpinge upon the emitter to cause the emitter to emit secondaryelectrons.

If the light source has a triple point made up of the first electrode,the emitter, and a vacuum atmosphere, then the primary electrons aredrawn from a portion of the first electrode near the triple point, andthe primary electrons drawn from the first electrode impinge upon theemitter to cause the emitter to emit secondary electrons. The secondaryelectrons referred to above include all electrons in a solid state whichgain energy by coulomb-attracted impingement of primary electrons andare expelled out of the emitter, auger electrons, and primary electrons(reflected electrons) scattered near the surface of the emitter. If thethickness of the first electrode is very small (up to 10 nm), thenelectrons are emitted from the interface between the first electrode andthe emitter.

Since electrons are emitted according to the above principles, the lightsource according to the present invention emits electrons stably 2billion times or more, and is highly practical. Furthermore, because theamount of emitted electrons increases substantially in proportion to thelevel of the drive voltage applied between the first electrode and thesecond electrode, the amount of emitted electrons can easily becontrolled.

The electrons attracted to the second electrode ionize a gas that ispresent primarily near the second electrode or atoms of the secondelectrode into positive ions and electrons. Atoms of the secondelectrode that are present near the second electrode are produced when aportion of the second electrode is evaporated, and are floating near thesecond electrode. Since the electrons produced by the above ionizationfurther ionize the gas and the atoms, the number of electrons isexponentially increased. When such a process goes on, electrons andpositive ions are present in a neutral fashion, developing a localplasma.

The positive ions produced by the ionization may impinge upon the firstelectrode, thus damaging the first electrode.

If the first electrode is disposed on a first surface of the emitter andthe second electrode is disposed on a second surface of the emitter,then the electrons emitted from the first electrode are attracted topositive poles of dipoles of the emitter that is present as a localanode, negatively charging the first surface of the emitter in thevicinity of the first electrode. As a result, the factor foraccelerating electrons (local potential difference) is lessened, nopotential is present for the emission of secondary electrons, and thefirst surface of the emitter is further negatively charged.

Therefore, the positive polarity of the local anode provided by thedipoles is reduced, and the intensity of the electric field between alocal anode and a local cathode is reduced, stopping the emission ofelectrons.

According to the present invention, therefore, the electron emitter isprevented from emitting excessive electrons to prevent the firstelectrode from being damaged by the emission of electrons, thus allowingthe light source with the electron emitter to have a long service lifeand increased reliability.

According to a fourth aspect of the present invention, there is furtherprovided a light source of the discharge lamp type, wherein electronsignite or assist in an electric discharge, a source of the electronscomprises an electron emitter, and the electron emitter comprises anemitter of a dielectric material and a first electrode and a secondelectrode to which a drive voltage is applicable to emit electrons fromthe emitter, the first electrode being disposed on a first surface ofthe emitter, the second electrode being disposed on a second surface ofthe emitter, at least the first electrode having a plurality of throughregions through which the emitter is exposed, and each of the throughregions has a peripheral portion having a surface facing the emitter andspaced from the emitter.

According to a fifth aspect of the present invention, there is furtherprovided a light source for emitting light by exciting a phosphor withan ultraviolet radiation generated from a gas sealed in a space in thelight source, wherein electrons assist in generating the ultravioletradiation from the gas, a source of the electrons comprises an electronemitter, and the electron emitter comprises an emitter of a dielectricmaterial and a first electrode and a second electrode to which a drivevoltage is applicable to emit electrons from the emitter, the firstelectrode being disposed on a first surface of the emitter, the secondelectrode being disposed on a second surface of the emitter, at leastthe first electrode having a plurality of through regions through whichthe emitter is exposed, and each of the through regions has a peripheralportion having a surface facing the emitter and spaced from the emitter.

According to a sixth aspect of the present invention, there is furtherprovided a light source for emitting light from a phosphor by havingelectrons and/or ions impinge upon the phosphor, the electrons and/orions being produced when electrons impinge upon molecules of a gassealed in a space in the light source and ionize the molecules of thegas, wherein a source of the electrons comprises an electron emitter,and the electron emitter comprises an emitter of a dielectric materialand a first electrode and a second electrode to which a drive voltage isapplicable to emit electrons from the emitter, the first electrode beingdisposed on a first surface of the emitter, the second electrode beingdisposed on a second surface of the emitter, at least the firstelectrode having a plurality of through regions through which theemitter is exposed, and each of the through regions has a peripheralportion having a surface facing the emitter and spaced from the emitter.

In the fourth through sixth aspects, the first electrode may emitelectrons toward the emitter to charge the emitter in a first stage, andthe emitter may emit electrons in a second stage.

Operation of the electron emitter according to the fourth through sixthaspects of the present invention will be described below. The drivevoltage is applied between the first electrode and the second electrode.The drive voltage is defined as a voltage, such as a pulse voltage or analternating-current voltage, which abruptly changes with time from avoltage level that is higher or lower than a reference voltage (e.g., 0V) to a voltage level that is lower or higher than the referencevoltage.

A triple junction is formed in a region of contact between the firstsurface of the emitter, the first electrode, and a medium (e.g., vacuum)around the electron emitter. The triple junction is defined as anelectric field concentration region formed by a contact between thefirst electrode, the emitter, and the vacuum. The triple junctionincludes a triple point where the first electrode, the emitter, and thevacuum exist as one point. According to the present invention, thetriple junction is formed in peripheral portions of a plurality ofthrough regions and the peripheral portion of the first electrode.Therefore, when the drive voltage is applied between the first electrodeand the second electrode, an electric field concentration occurs at thetriple junction.

In the first stage, the voltage higher or lower than the referencevoltage is applied between the first electrode and the second electrode,producing an electric field concentration in one direction, for example,at the triple junction. Electrons are emitted from the first electrodetoward the emitter, and accumulated in the portions of the emitter whichcorrespond to the through regions of the first electrode and the portionof the emitter near the peripheral portion of the first electrode. Thatis, the emitter is charged. At this time, the first electrode functionsas an electron supply source.

In the second stage, the voltage level of the drive voltage abruptlychanges, i.e., the voltage lower or higher than the reference voltage isapplied between the first electrode and the second electrode. Theelectrons that have been accumulated in the portions corresponding tothe through regions of the first electrode and the regions near theperipheral portion of the first electrode are expelled from the emitterby dipoles (whose negative poles appear on the surface of the emitter)in the emitter whose polarization has been inverted in the oppositedirection. The electrons are emitted from the portions of the emitterwhere the electrons have been accumulated, through the through regions.The electrons are also emitted from the regions near the outerperipheral portion of the first electrode. At this time, electronsdepending on the amount of charges in the emitter in the first stage areemitted from the emitter in the second stage. The amount of charges inthe emitter in the first stage is maintained until electrons are emittedin the second stage.

With the electron emitter, since the first electrode has the pluralthrough regions, electrons are uniformly emitted from each of thethrough regions and the regions near the outer peripheral portions ofthe first electrode. Thus, any variations in the overall electronemission characteristics are reduced, making it possible to facilitatethe control of the electron emission and increase the electron emissionefficiency.

According to the fourth through sixth aspects of the present invention,because a gap is formed between the surface of the first electrode whichfaces the emitter around the through regions and the emitter, when thedrive voltage is applied, an electric field concentration tends to beproduced in the region of the gap. This leads to a higher efficiency ofthe electron emission, making the drive voltage lower (emittingelectrons at a lower voltage level).

As described above, according to the fourth through sixth aspects of thepresent invention, since the first electrode has an overhanging portion(flange) on the peripheral portion of each through region, together withthe increased electric field concentration in the region of the gap,electrons are easily emitted from the overhanging portion (around thethrough region). This leads to a larger output and higher efficiency ofthe electron emission, making the drive voltage lower. As the peripheryof the through region functions as a gate electrode (a controlelectrode, a focusing electronic lens, or the like), the straightness ofemitted electrons can be increased. This is effective in reducingcrosstalk if a number of electron emitters are arrayed for use as anelectron source of displays.

As described above, according to the fourth through sixth aspects of thepresent invention, the light source is capable of easily developing ahigh electric field concentration, provides many electron emissionregions, has a larger output and higher efficiency of the electronemission, and can be driven at a lower voltage (lower powerconsumption).

The light sources according to the first through sixth aspects of thepresent invention may have means for applying AC pulses between thefirst electrode and the second electrode to cause at least a portion ofthe emitter to have its polarization inverted or changed, whereinelectrons are intermittently emitted from the emitter. Before lightemitted by a first emission of electrons is extinguished, next electronsmay be emitted to emit light continuously.

The light sources according to the first through sixth aspects of thepresent invention may have a third electrode at a position correspondingto the first electrode above the emitter, and the third electrode may becoated with a phosphor. Some of the emitted electrons are attracted tothe third electrode and excite the phosphor, which emits fluorescentlight.

The light sources according to the first through sixth aspects of thepresent invention may have a phosphor disposed around the electronemitter, and mercury particles, for example, may be sealed in theatmosphere between the electron emitter and the phosphor. Some of theemitted electrons impinge upon the mercury particles, which are excitedto emit ultraviolet rays. The ultraviolet rays hit the phosphor, whichis excited to emit fluorescent light.

In the above arrangement, a plurality of electron emitters may bearranged in a two-dimensional array, realizing a planar light sourcecomprising electron emitters and having a longer service life andincreased reliability.

Advantages of planar light sources will be described below in terms oftheir differences with displays. Unlike a display, a planar light sourcemay emit light from its entire surface at all times, and hence does notneed to be driven under complex control such as row scanning control,etc., but may be driven altogether statically. Since the diameter of alight emission spot produced by an electron emission does not need to becontrolled, it is not necessary to install a control electrode, etc.functioning as a focusing lens, for example, between the electronemitters and the phosphors. This leads to a simplified mechanicalarrangement and a simplified circuit arrangement.

The display needs to handle a data signal that changes at a high speeddepending on the pixel signal. Therefore, the drive voltage is of acomplex waveform that is modulated depending on the gradation. On theother hand, as the planar light source is not required to handle a datasignal that changes at a high speed depending on the pixel signal, thedrive voltage may be of a simple waveform, i.e., a waveform having aconstant pulse period or pulse duration. As a result, if an electricpower retrieval circuit is connected to the planar light source, notonly the circuit constants, circuit switching timing, etc. of theelectric power retrieval circuit can be set with high accuracy, but alsoalmost 100% of the drive voltage can be retrieved.

The electron emitters may be divided into two groups, and when theelectron emitters in one of the groups emit light, the electron emittersin the other group may retrieve electric power of the electron emittersin the one group, and when the electron emitters in the other group emitlight, the electron emitters in the one group may retrieve electricpower of the electron emitters in the other group.

Consequently, the electron emitters in the group other than the groupwhich is emitting light double as a buffer capacitor for retrievingelectric power. Therefore, no separate buffer capacitor is required, andhence the light source may be mounted in a reduced area and may consumereduced electric power.

In the above arrangement, the drive voltage may be modulated based on acontrol signal to control an amount of electrons emitted from theelectron emitter for controlling emitted light.

The light sources according to the first through sixth aspects of thepresent invention may have at least two planar light source sections,and each of the planar light source sections may have a plurality of theelectron emitters which are arranged in a two-dimensional array.

Thus, each of the planar light source sections can be controlled forenergization/de-energization to perform stepwise light control (digitallight control). Particularly, if the light source has means formodulating the drive voltage applied to each of the electron emitters ineach of the planar light source sections based on a correspondingcontrol signal to control the amount of electrons emitted from theelectron emitter for performing light control of each of the planarlight source sections, then the light emission distributions of theplanar light source sections can independently be controlled. That is,the light source can perform analog light control as well as digitallight control for fine light control applications.

The electron emitters of each of the planar light source sections may bedivided into two groups, and when the electron emitters in one of thegroups emit light, the electron emitters in the other group may retrieveelectric power of the electron emitters in the one group, and when theelectron emitters in the other group emit light, the electron emittersin the one group may retrieve electric power of the electron emitters inthe other group.

Furthermore, at least two planar light source sections may be dividedinto two groups, and when the electron emitters in one of the groupsemit light, the electron emitters in the other group may retrieveelectric power of the electron emitters in the one group, and when theelectron emitters in the other group emit light, the electron emittersin the one group may retrieve electric power of the electron emitters inthe other group.

With the light sources according to the present invention, the electronemitter having the emitter made of a dielectric material is preventedfrom emitting excessive electrons to prevent the electrode from beingdamaged by the emission of electrons, thus allowing the light source tohave a long service life and increased reliability.

Moreover, the light sources are capable of easily developing a highelectric field concentration, provide many electron emission regions,have a larger output and higher efficiency of the electron emission, andcan be driven at a lower voltage.

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which preferredembodiments of the present invention are shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary cross-sectional view, partly in block form, of alight source according to a first embodiment of the present invention;

FIG. 2A is a plan view of electrodes of an electron emitter;

FIG. 2B is a plan view of electrodes according to a first modification;

FIG. 3 is a plan view of electrodes according to a second modification;

FIG. 4 is a waveform diagram showing a drive voltage output from a drivecircuit;

FIG. 5 is a fragmentary cross-sectional view illustrative of the mannerin which a voltage Va1 is applied between an upper electrode and a lowerelectrode in the first embodiment;

FIG. 6 is a fragmentary cross-sectional view illustrative of an electronemission when a voltage Va2 is applied between the upper electrode andthe lower electrode;

FIG. 7 is a fragmentary cross-sectional view illustrative of aself-inactivation of an electron emission due to a negative charge onthe surface of an emitter;

FIG. 8 is a characteristic diagram showing the relationship between theenergy of emitted secondary electrons and the quantity of emittedsecondary electrons;

FIG. 9A is a waveform diagram of a drive voltage;

FIG. 9B is a waveform diagram showing a change in the voltage betweenthe upper electrode and the lower electrode of the electron emitteraccording to the first embodiment;

FIG. 10 is a fragmentary cross-sectional view, partly in block form, ofa first modification of the light source according to the firstembodiment of the present invention;

FIG. 11 is a fragmentary cross-sectional view, partly in block form, ofa second modification of the light source according to the firstembodiment of the present invention;

FIG. 12 is a block diagram of a drive circuit;

FIG. 13A is a waveform diagram showing a control signal representativeof turn-on/turn-off;

FIG. 13B is a waveform diagram showing a clock signal;

FIG. 13C is a waveform diagram showing timing pulses;

FIG. 13D is a waveform diagram showing a drive voltage generated by adrive voltage generating circuit;

FIG. 14 is a circuit diagram, partly in block form, showing a conceptualrepresentation of a drive circuit according to a preferred embodiment ofthe present invention;

FIG. 15 is a waveform diagram illustrative of operation of the drivecircuit;

FIG. 16 is a view of a third modification of the light source accordingto the first embodiment of the present invention;

FIG. 17 is a waveform diagram illustrative of operation of a drivecircuit for the light source according to the third modification;

FIG. 18 is a block diagram of a drive circuit according to amodification;

FIG. 19A is a waveform diagram showing a light control signal;

FIG. 19B is a diagram illustrative of a process of modulating a periodT2 depending on the voltage level of the light control signal;

FIG. 19C is a diagram illustrative of a process of modulating a periodin which to apply the voltage Va2 (pulse duration) depending on thevoltage level of the light control signal;

FIG. 20 is a characteristic diagram showing the relationship between thepulse duration of the voltage Va2 and luminance;

FIG. 21 is a characteristic diagram showing the relationship between acollector voltage and luminance;

FIG. 22 is a characteristic diagram showing the relationship between thevoltage Va2 (voltage level) applied between the upper electrode and thelower electrode and luminance;

FIG. 23 is a characteristic diagram showing the relationship between thevoltage Va1 applied between the upper electrode and the lower electrodeand luminance;

FIG. 24 is a circuit diagram of a fourth modification of the lightsource according to the first embodiment of the present invention;

FIG. 25 is a cross-sectional view of an electron emitter of the lightsource according to the fourth modification;

FIG. 26 is a circuit diagram showing an equivalent circuit of theelectron emitter shown in FIG. 25, primarily in terms of a currentflowing between the upper electrode and the collector electrode;

FIG. 27 is a diagram showing the output characteristics (Vkc-Ikccharacteristics) of the electron emitter shown in FIG. 25;

FIG. 28 is a circuit diagram showing an equivalent circuit of anarrangement in which a control electrode is disposed between the upperelectrode and the collector electrode, in terms of a collector currentflowing through the collector electrode and a control current flowingthrough the control electrode;

FIG. 29 is a view, partly in block form, of a fifth modification of thelight source according to the first embodiment;

FIG. 30 is a view of a sixth modification of the light source accordingto the first embodiment;

FIG. 31 is a view, partly in block form, of a seventh modification ofthe light source according to the first embodiment;

FIG. 32 is a view, partly in block form, of an eighth modification ofthe light source according to the first embodiment;

FIG. 33 is a fragmentary cross-sectional view of a ninth modification ofthe light source according to the first embodiment;

FIG. 34 is a fragmentary cross-sectional view of a tenth modification ofthe light source according to the first embodiment;

FIG. 35 is a fragmentary cross-sectional view of an eleventhmodification of the light source according to the first embodiment;

FIG. 36 is a fragmentary cross-sectional view of a twelfth modificationof the light source according to the first embodiment;

FIG. 37 is a fragmentary cross-sectional view of a thirteenthmodification of the light source according to the first embodiment;

FIG. 38 is a fragmentary cross-sectional view of electron emitters usedin a light source according to a second embodiment of the presentinvention;

FIG. 39 is an enlarged fragmentary cross-sectional view of an electronemitter;

FIG. 40 is a plan view showing an example of the shape of throughregions defined in an upper electrode;

FIG. 41A is a cross-sectional view of another example of the upperelectrode;

FIG. 41B is an enlarged fragmentary cross-sectional view of the upperelectrode;

FIG. 42A is a cross-sectional view of still another example of the upperelectrode;

FIG. 42B is an enlarged fragmentary cross-sectional view of the upperelectrode;

FIG. 43 is a diagram showing the voltage waveform of a drive voltage ina first electron emission process;

FIG. 44 is a view illustrative of the emission of electrons in a secondoutput period of the first electron emission process;

FIG. 45 is a diagram showing the voltage waveform of a drive voltage ina second electron emission process;

FIG. 46 is a view illustrative of the emission of electrons in a secondoutput period of the second electron emission process;

FIG. 47 is a view showing a cross-sectional shape of an overhangingportion of the upper electrode;

FIG. 48 is a view showing a cross-sectional shape of another overhangingportion of the upper electrode;

FIG. 49 is a view showing a cross-sectional shape of still anotheroverhanging portion of the upper electrode;

FIG. 50 is an equivalent circuit diagram showing a connected state ofvarious capacitors connected between the upper electrode and the lowerelectrode;

FIG. 51 is a diagram illustrative of calculations of capacitances of thevarious capacitors connected between the upper electrode and the lowerelectrode;

FIG. 52 is a fragmentary plan view of an electron emitter according to afirst modification which can be used in the light source according tothe second embodiment;

FIG. 53 is a fragmentary plan view of an electron emitter according to asecond modification which can be used in the light source according tothe second embodiment;

FIG. 54 is a fragmentary cross-sectional view of an electron emitteraccording to a third modification which can be used in the light sourceaccording to the second embodiment;

FIG. 55 is a diagram showing the voltage vs. charge quantitycharacteristics (voltage vs. polarized quantity characteristics) of anelectron emitter used in the light source according to the secondembodiment of the present invention;

FIG. 56A is a view illustrative of a state at a point p1 shown in FIG.55;

FIG. 56B is a view illustrative of a state at a point p2 shown in FIG.55;

FIG. 56C is a view illustrative of a state from the point p2 to a pointp3 shown in FIG. 55;

FIG. 57A is a view illustrative of a state from the point p3 to a pointp4 shown in FIG. 55;

FIG. 57B is a view illustrative of a state immediately prior to a pointp4 shown in FIG. 55;

FIG. 57C is a view illustrative of a state from the point p4 to a pointp6 shown in FIG. 55;

FIG. 58 is a block diagram of a display area and a drive circuit thatare used in the light source according to the second embodiment;

FIGS. 59A through 59C are waveform diagrams illustrative of theamplitude modulation of pulse signals by an amplitude modulatingcircuit;

FIG. 60 is a block diagram of a signal supply circuit according to amodification;

FIGS. 61A through 61C are waveform diagrams illustrative of the pulsewidth modulation of pulse signals by a pulse width modulating circuit;

FIG. 62A is a diagram showing a hysteresis curve plotted when a voltageVsl shown in FIG. 59A or 61A is applied;

FIG. 62B is a diagram showing a hysteresis curve plotted when a voltageVsm shown in FIG. 59B or 61B is applied;

FIG. 62C is a diagram showing a hysteresis curve plotted when a voltageVsh shown in FIG. 59C or 61C is applied;

FIG. 63 is a view showing a layout of a collector electrode, a phosphor,and a transparent plate on the upper electrode;

FIG. 64 is a view showing another layout of a collector electrode, aphosphor, and a transparent plate on the upper electrode;

FIG. 65A is a diagram showing the waveform of a write pulse and aturn-on pulse that are used in a first experimental example (anexperiment for observing the emission of electrons from an electronemitter);

FIG. 65B is a diagram showing the waveform of a detected voltage of alight-detecting device, which is representative of the emission ofelectrons from the electron emitter in the first experimental example;

FIG. 66 is a diagram showing the waveform of a write pulse and a turn-onpulse that are used in second through fourth experimental examples;

FIG. 67 is a characteristic diagram showing the results of a secondexperimental example (an experiment for observing how the amount ofelectrons emitted from the electron emitter changes depending on theamplitude of a write pulse);

FIG. 68 is a characteristic diagram showing the results of a thirdexperimental example (an experiment for observing how the amount ofelectrons emitted from the electron emitter changes depending on theamplitude of a turn-on pulse);

FIG. 69 is a characteristic diagram showing the results of a fourthexperimental example (an experiment for observing how the amount ofelectrons emitted from the electron emitter changes depending on thelevel of a collector voltage);

FIG. 70 is a timing chart illustrative of a drive method for the lightsource;

FIG. 71 is a diagram showing the relationship of applied voltagesaccording to the drive method shown in FIG. 70;

FIG. 72 is a fragmentary cross-sectional view of an electron emitteraccording to a first modification which can be used in the light sourceaccording to the second embodiment;

FIG. 73 is a fragmentary cross-sectional view of an electron emitteraccording to a second modification which can be used in the light sourceaccording to the second embodiment;

FIG. 74 is a fragmentary cross-sectional view of an electron emitteraccording to a third modification which can be used in the light sourceaccording to the second embodiment;

FIG. 75 is a fragmentary cross-sectional view of an electron emitteraccording to a fourth modification which can be used in the light sourceaccording to the second embodiment;

FIG. 76 is a fragmentary cross-sectional view of an electron emitteraccording to a fifth modification which can be used in the light sourceaccording to the second embodiment;

FIG. 77 is a fragmentary cross-sectional view of an electron emitteraccording to a sixth modification which can be used in the light sourceaccording to the second embodiment;

FIG. 78 is a fragmentary perspective view of a light source according toa third embodiment of the present invention;

FIG. 79 is a perspective view of an array of electron emission units inthe light source according to the third embodiment;

FIG. 80 is an enlarged fragmentary perspective view of an encircledportion Lc in FIG. 79;

FIG. 81 is a waveform diagram showing light emission pulse widths in thelight source according to the third embodiment;

FIG. 82 is a fragmentary perspective view of a light source according toa fourth embodiment of the present invention;

FIG. 83 is a fragmentary perspective view of a light source according toa fifth embodiment of the present invention;

FIG. 84 is a fragmentary perspective view showing an array of electronemitters, white phosphors, and an anode electrode in the light sourceaccording to the fifth embodiment; and

FIG. 85 is an enlarged fragmentary perspective view of an encircledportion Ld in FIG. 84.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Light sources according to embodiments of the present invention will bedescribed below with reference to FIGS. 1 through 85.

As shown in FIG. 1, a light source 10A according to a first embodimentof the present invention has a light emitting section 14A comprising atwo-dimensional array of electron emitters 12A, and a drive circuit 16Afor applying a drive voltage Va to each of the electron emitters 12A ofthe light emitting section 14A.

The drive circuit 16A applies a drive voltage Va between a firstelectrode (e.g., an upper electrode) 18 and a second electrode (e.g., alower electrode) 20 of each of the electron emitters 12A to control eachof the electron emitters 12A based on a control signal Sc representativeof turn-on/turn-off from an external source (a turn-on/turn-off switchor the like). Preferred examples of the drive circuit 16A will bedescribed later on.

As shown in FIG. 1, each of the electron emitters 12A has a plate-likeemitter 22, the upper electrode 18 disposed on a face side of theemitter 22, and the lower electrode 20 disposed on a reverse side of theemitter 22. Since the electron emitter 12A is of a structure in whichthe emitter 22 is sandwiched between the upper electrode 18 and thelower electrode 20, it provides a capacitive load. Therefore, theelectron emitter 12A may be regarded as a capacitor C (see FIG. 12).

A drive voltage Va from the drive circuit 16A is applied between theupper electrode 18 and the lower electrode 20. In FIG. 1, the lowerelectrode 20 is connected to GND (ground) through a resistor R1, andhence is kept at the zero potential. However, the lower electrode 20 maybe held at a potential other than the zero potential. As shown in FIGS.2A and 2B, for example, the drive voltage Va is applied between theupper electrode 18 and the lower electrode 20 through a lead electrode24 connected to the upper electrode 18 and a lead electrode 26 connectedto the lower electrode 20.

As shown in FIG. 1, if the electron emitters 12A are used as a lightsource, then a transparent panel 30 of glass or acrylic resin is placedover the upper electrodes 18, and a collector electrode 32 comprising atransparent electrode, for example, is mounted on the reverse side ofthe transparent panel 30, i.e., the surface of the transparent panel 30which faces the upper electrodes 18. The collector electrode 32 iscoated with a phosphor 34. A bias power supply 36 having a bias voltageVc is connected to the collector electrode 32 through a resistor R2.

The electron emitters 12A are placed in a vacuum. As shown in FIG. 1,electric field concentration points A are present in each of theelectron emitters 12A. Each of the electric field concentration points Amay be defined as a point including a triple point where the upperelectrode 18, the emitter 22, the vacuum exist.

The vacuum level in the atmosphere should preferably in the range from10² to 10⁻⁶ Pa and more preferably in the range from 10⁻³ to 10⁻⁵ Pa.

The reason for the above range is that in a lower vacuum, (1) many gasmolecules would be present in the space, and a plasma can easily begenerated and, if too an intensive plasma were generated, many positiveions thereof would impinge upon the upper electrode 18 and damage thesame, and (2) emitted electrons would tend to impinge upon gas moleculesprior to arrival at the collector electrode 32, failing to sufficientlyexcite the phosphor 34 with electrons that are sufficiently acceleratedunder the collector voltage Vc.

In a higher vacuum, though electrons would be liable to be emitted froman electric field concentration point A, structural body supports andvacuum seals would be large in size, posing disadvantages on efforts tomake the electron emitter smaller in size.

The emitter 22 is made of a dielectric material. The dielectric materialmay preferably be a dielectric material having a relatively highdielectric constant, e.g., a dielectric constant of 1000 or higher.Dielectric materials of such a nature may be ceramics including bariumtitanate, lead zirconate, lead magnesium niobate, lead nickel niobate,lead zinc niobate, lead manganese niobate, lead magnesium tantalate,lead nickel tantalate, lead antimony tinate, lead titanate, leadmagnesium tungstenate, lead cobalt niobate, etc. or a combination of anyof these materials, a material which chiefly contains 50 weight % ormore of any of these materials, or such ceramics to which there is addedan oxide of such as lanthanum, calcium, strontium, molybdenum, tungsten,barium, niobium, zinc, nickel, manganese, or the like, or a combinationof these materials, or any of other compounds.

For example, a two-component material nPMN-mPT (n, m represent molarratios) of lead magnesium niobate (PMN) and lead titanate (PT) has itsCurie point lowered for a larger specific dielectric constant at roomtemperature if the molar ratio of PMN is increased.

Particularly, a dielectric material where n=0.85−1.0 and m=1.0−n ispreferable because its specific dielectric constant is 3000 or higher.For example, a dielectric material where n=0.91 and m=0.09 has aspecific dielectric constant of 15000 at room temperature, and adielectric material where n=0.95 and m=0.05 has a specific dielectricconstant of 20000 at room temperature.

For increasing the specific dielectric constant of a three-componentdielectric material of lead magnesium niobate (PMN), lead titanate (PT),and lead zirconate (PZ), it is preferable to achieve a composition closeto a morphotropic phase boundary (MPB) between a tetragonal system and aquasi-cubic system or a tetragonal system and a rhombohedral system, aswell as to increase the molar ratio of PMN. For example, a dielectricmaterial where PMN:PT PZ=0.375:0.375:0.25 has a specific dielectricconstant of 5500, and a dielectric material wherePMN:PT:PZ=0.5:0.375:0.125 has a specific dielectric constant of 4500,which is particularly preferable. Furthermore, it is preferable toincrease the dielectric constant by introducing a metal such as platinuminto these dielectric materials within a range to keep them insulative.For example, a dielectric material may be mixed with 20 weight % ofplatinum.

The emitter 22 may be in the form of a piezoelectric/electrostrictivelayer or an anti-ferroelectric layer. If the emitter 22 comprises apiezoelectric/electrostrictive layer, then it may be made of ceramicssuch as lead zirconate, lead magnesium niobate, lead nickel niobate,lead zinc niobate, lead manganese niobate, lead magnesium tantalate,lead nickel tantalate, lead antimony tinate, lead titanate, bariumtitanate, lead magnesium tungstenate, lead cobalt niobate, or the like,or a combination of any of these materials.

The emitter 22 may be made of chief components including 50 wt % or moreof any of the above compounds. Of the above ceramics, the ceramicsincluding lead zirconate is mostly frequently used as a constituent ofthe piezoelectric/electrostrictive layer of the emitter 22.

If the piezoelectric/electrostrictive layer is made of ceramics, thenlanthanum, calcium, strontium, molybdenum, tungsten, barium, niobium,zinc, nickel, manganese, or the like, or a combination of thesematerials, or any of other compounds may be added to the ceramics.Alternatively, ceramics produced by adding SiO₂, CeO₂, Pb₅Ge₃O₁₁, or acombination of any of these compounds to the above ceramics may be used.Specifically, a material produced by adding 0.2 wt % of SiO₂, 0.1 wt %of CeO₂, or 1 to 2 wt % of Pb₅Ge₃₀₁₁ to a PT-PZ-PMN piezoelectricmaterial is preferable.

For example, the piezoelectric/electrostrictive layer should preferablybe made of ceramics including as chief components lead magnesiumniobate, lead zirconate, and lead titanate, and also including lanthanumand strontium.

The piezoelectric/electrostrictive layer may be dense or porous. If thepiezoelectric/electrostrictive layer is porous, then it shouldpreferably have a porosity of 40% or less.

If the emitter 22 is in the form of an anti-ferroelectric layer, thenthe anti-ferroelectric layer may be made of lead zirconate as a chiefcomponent, lead zirconate and lead tin as chief components, leadzirconate with lanthanum oxide added thereto, or lead zirconate and leadtin as components with lead zirconate and lead niobate added thereto.

The anti-ferroelectric layer may be porous. If the anti-ferroelectriclayer is porous, then it should preferably have a porosity of 30% orless.

If the emitter 22 is made of strontium tantalate bismuthate(SrBi₂Ta₂O₉), then its polarization inversion fatigue is small.Materials whose polarization inversion fatigue is small are laminarferroelectric compounds and expressed by the general formula of (BiO₂)²⁺(A_(m-1)B_(m)O_(3m+1))²⁻ Ions of the metal A are Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺,Bi³⁺, La³⁺, etc., and ions of the metal B are Ti⁴⁺, Ta⁵⁺, Nb⁵⁺, etc. Anadditive may be added to piezoelectric ceramics of barium titanate, leadzirconate, and PZT to convert them into a semiconductor. In this case,it is possible to provide an irregular electric field distribution inthe emitter 22 to concentrate an electric field in the vicinity of theinterface with the upper electrode 18 which contributes to the emissionof electrons.

The baking temperature can be lowered by adding glass such as leadborosilicate glass or the like or other compounds of low melting point(e.g., bismuth oxide or the like) to thepiezoelectric/electrostrictive/anti-ferroelectric ceramics.

If the emitter 22 is made ofpiezoelectric/electrostrictive/anti-ferroelectric ceramics, then it maybe a sheet-like molded body, a sheet-like laminated body, or either oneof such bodies stacked or bonded to another support substrate.

If the emitter 22 is made of a non-lead-based material, then it may be amaterial having a high melting point or a high evaporation temperatureso as to be less liable to be damaged by the impingement of electrons orions.

The emitter 22 may be made by any of various thick-film formingprocesses including screen printing, dipping, coating, electrophoresis,aerosol deposition, etc., or any of various thin-film forming processesincluding an ion beam process, sputtering, vacuum evaporation, ionplating, chemical vapor deposition (CVD), plating, etc. Particularly, itis preferable to form a powdery piezoelectric/electrostrictive materialas the emitter 22 and impregnate the emitter 22 thus formed with glassof a low melting point or sol particles. According to this process, itis possible to form a film at a low temperature of 700° C. or lower or600° C. or lower.

The magnitude of the thickness d (see FIG. 1) of the emitter 22 betweenthe upper electrode 18 and the lower electrode 20 will be describedbelow. If the voltage between the upper electrode 18 and the lowerelectrode 20, i.e., the voltage that appears between the upper electrode18 and the lower electrode 20 when the drive voltage Va output from thedrive circuit 16A is applied between the upper electrode 18 and thelower electrode 20, is represented by Vak, then it is preferable toestablish the thickness d such that a polarization inversion or apolarization change occurs with an electric field E expressed byE=Vak/d. That is, as the thickness d is smaller, a polarization reversalor a polarization change can occur at a lower voltage, enabling theelectron emitter to emit electrons when driven by a lower voltage, e.g.,less than 100 V.

The upper electrode 18 should preferably be made of a conductor having asmall sputtering yield and a high evaporation temperature in vacuum. Forexample, materials having a sputtering yield of 2.0 or less at 600 V inAr⁺ and an evaporation pressure of 1.3×10⁻³ Pa at a temperature of 1800K or higher are preferable. Such materials include platinum, molybdenum,tungsten, etc. The upper electrode 18 may be made of a conductor whichis resistant to a high-temperature oxidizing atmosphere, e.g., a metal,an alloy, a mixture of insulative ceramics and a metal, or a mixture ofinsulative ceramics and an alloy. Preferably, the upper electrode 18should be chiefly composed of a precious metal having a high meltingpoint, e.g., platinum, iridium, palladium, rhodium, molybdenum, or thelike, or an alloy of silver and palladium, silver and platinum, platinumand palladium, or the like, or a cermet of platinum and ceramics.Further preferably, the upper electrode 18 should be made of platinumonly or a material chiefly composed of a platinum-base alloy. Theelectrodes should preferably be made of carbon or a graphite-basematerial, e.g., diamond thin film, diamond-like carbon, or carbonnanotube. Ceramics to be added to the electrode material shouldpreferably have a proportion ranging from 5 to 30 volume %.

Furthermore, the upper electrode 18 should preferably be made of anorganic metal paste which can produce a thin film after being baked. Forexample, a platinum resinate paste or the like, should preferably beused. An oxide electrode for suppressing a polarization inversionfatigue, which is made of ruthenium oxide, iridium oxide, strontiumruthenate, La_(1-x)Sr_(x)CoO₃ (e.g., x=0.3 or 0.5), La_(1-x)Ca_(x)MnO₃,La_(1-x)Ca_(x)Mn_(1-y)CO_(y)O₃ (e.g., x=0.2, y=0.05), or a mixture ofany one of these compounds and a platinum resinate paste, for example,is preferable.

The upper electrode 18 may be made of any of the above materials by anyof thick-film forming processes including screen printing, spraycoating, coating, dipping, electrophoresis, etc., or any of variousthin-film forming processes including sputtering, an ion beam process,vacuum evaporation, ion plating, chemical vapor deposition (CVD),plating, etc. Preferably, the upper electrode 18 is made by any of theabove thick-film forming processes.

The shape in plan of the upper electrode 18 may be an elliptical shapeas shown in FIG. 2A, or a ring shape as with an electron emitter 12Aaaccording to a first modification shown in FIG. 2B. Alternatively, theshape in plan of the upper electrode 18 may be a comb-toothed shape aswith an electron emitter 12Ab according to a second modification shownin FIG. 3.

The ring-shaped or comb-toothed upper electrode 18 is effective toincrease the number of triple points of the upper electrode 18, theemitter 22, and the vacuum as electric field concentration points A forincreased electron emission efficiency.

The upper electrode 18 should preferably have a thickness tc (seeFIG. 1) of 20 μm or less or preferably of 5 μm or less. Therefore, thethickness tc of the upper electrode 18 may be 100 nm or less. If thethickness tc of the upper electrode 18 is extremely small (10 nm orless), then electrons are emitted from the interface between the upperelectrode 18 and the emitter 22 for further increased electron emissionefficiency.

The lower electrode 20 is made of the same material according to thesame process as the upper electrode 18. Preferably, the lower electrode20 is made according to one of the above thick-film forming processes.The lower electrode 20 should preferably have a thickness of 20 μm orless or preferably of 5 μm or less.

Each time the emitter 22, the upper electrode 18, or the lower electrode20 is formed, the assembly is heated (sintered) into an integralstructure. Depending on how the upper electrode 18 and the lowerelectrode 20 are formed, however, the heating (sintering) process forproducing an integral structure may not be required.

The sintering process for integrally combining the emitter 22, the upperelectrode 18, and the lower electrode 20 may be carried out at atemperature ranging from 500° to 1400° C., preferably from 1000° to1400° C. For heating the emitter 22 which is in the form of a film, theemitter 22 should preferably be sintered together with its evaporationsource while their atmosphere is being controlled, so that thecomposition of the emitter 22 will not become unstable at hightemperatures.

The emitter 22 may be covered with a suitable member, and then sinteredsuch that the surface of the emitter 22 will not be exposed directly tothe sintering atmosphere.

The principles of electron emission of the electron emitter 12A will bedescribed below with reference to FIGS. 1, 4 through 9B. First, as shownin FIG. 4, a drive voltage Va output from the drive circuit 16A hasrepeated steps each including a period T1, in which a voltage Va1 makingthe potential of the upper electrode 18 higher than the potential of thelower electrode 20, is output and a period T2, in which a voltage Va2making the potential of the upper electrode 18 lower than the potentialof the lower electrode 20, is output. The voltage Va2 which is output inthe period T2 is referred to as a drive pulse Pd.

The drive pulse Pd has an amplitude Vin that is defined as a valueproduced by subtracting the voltage Va2 from the voltage Va1(=Va1−Va2).

The period T1 is a period in which the voltage Va1 is applied betweenthe upper electrode 18 and the lower electrode 20 to polarize theemitter 22, as shown in FIG. 5. The voltage Va1 may be a DC voltage, asshown in FIG. 4, but may be a single pulse voltage or a succession ofpulse voltages. The period T1 should preferably be longer than theperiod T2 for sufficient polarization. For example, the period T1 shouldpreferably be of 100 μsec. or longer. This is because the absolute valueof the voltage Va1 for polarization is set so as to be smaller than theabsolute value of the voltage Va2 for the purpose of lowering the powerconsumption at the time the voltage Va1 is applied and preventing damageto the upper electrode 18.

The voltages Va1, Va2 should preferably be of such voltage levels as tobe able to polarize the emitter 22 reliably into positive and negativepoles. For example, if the dielectric material of the emitter 22 has acoercive voltage, then the absolute values of the voltages Va1, Va2should preferably be equal to or higher than the coercive voltage.

When the drive pulse Pd, having an amplitude of a predetermined level,is applied between the upper electrode 18 and the lower electrode 20,the polarization is inverted or changed in at least a portion of theemitter 22, as shown in FIG. 6. The portion of the emitter 22 where thepolarization is inverted or changed includes a portion directly belowthe upper electrode 18 and a portion whose surface is exposed in thevicinity of the upper electrode 18, because the polarization seeps inthe portion of the emitter 22 whose surface is exposed in the vicinityof the upper electrode 18. When the polarization is inverted or changed,a local electric field concentration occurs at the upper electrode 18and the positive poles of the dipole moments near the upper electrode18, drawing primary electrons from the upper electrode 18. The primaryelectrons from the upper electrode 18 impinge upon the emitter 22,causing the emitter 22 to emit secondary electrons.

If the electron emitter 12A has a triple point A of the upper electrode18, the emitter 22, and the vacuum in the present embodiment, primaryelectrons are drawn from the portion of the upper electrode 18 near thetriple point A, and the primary electrons drawn from the triple point Aimpinge upon the emitter 22, which emits secondary electrons. If thethickness of the upper electrode 18 is very small (up to 10 nm), thenelectrons are emitted from the interface between the upper electrode 18and the emitter 22.

Operation of the electron emitter 12A at the time a drive pulse Pdhaving an amplitude of a predetermined level is applied will bedescribed in greater detail below.

When a drive pulse Pd, having an amplitude of a predetermined level, isapplied between the upper electrode 18 and the lower electrode 20,secondary electrons are emitted from the emitter 22, as described above.That is, those dipole moments which, are charged in the emitter 22 inthe vicinity of the upper electrode 18, have their positive polesserving as a local anode, drawing electrons from the upper electrode 18.Some of the drawn electrons are attracted to the collector electrode 32(see FIG. 1) and excite the phosphor 34, which emits fluorescent light.Some of the drawn electrons impinge upon the emitter 22, which emitsecondary electrons that are attracted to the collector electrode 32 andexcite the phosphor 34.

A distribution of the emitted secondary electrons will be describedbelow with reference to FIG. 8. As shown in FIG. 8, most of thesecondary electrons have an energy level which is nearly zero. When theyare emitted from the surface of the emitter 22 into the vacuum, theymove according to a surrounding electric field distribution only.Specifically, the secondary electrons are accelerated from an initialvelocity of almost 0 (m/sec.) according to the surrounding electricfield distribution. Therefore, as shown in FIG. 1, if an electric fieldEa occurs between the emitter 22 and the collector electrode 32, thenthe secondary electrons have their trajectory determined along theelectric field Ea. That is, an electron source, which emits electronsstraightly, is realized. The secondary electrons with the low initialvelocity are electrons in solid state which gain energy bycoulomb-attracted impingement of primary electrons and are expelled outof the emitter 22.

As can be seen from FIG. 8, secondary electrons having an energy levelcorresponding to the energy E₀ of primary electrons are emitted. Thesesecondary electrons are primary electrons emitted from the upperelectrode 18 and scattered in the vicinity of the surface of the emitter22 (reflected electrons). The secondary electrons referred to in thepresent specification are defined as including such reflected electronsand Auger electrons.

If the thickness of the upper electrode 18 is very small (up to 10 nm),then primary electrons emitted from the upper electrode 18 are reflectedby the interface between the upper electrode 18 and the emitter 22 anddirected toward the collector electrode 32.

As shown in FIG. 6, the intensity E_(A) Of the electric field at theelectric field concentration point A is expressed by E_(A)=V(1 a, 1k)/d_(A) where V(1 a, 1 k) represents the potential difference between alocal anode and a local cathode and d_(A) the distance between a localanode and a local cathode. Since the distance d_(A) between a localanode and a local cathode is very small, the intensity E_(A) of theelectric field which is required to emit electrons can easily beachieved (in FIG. 6, an increase in the intensity E_(A) of the electricfield is indicated by the solid-line arrow). This leads to a reductionin a voltage Vak.

As the emission of electrons from the upper electrode 18 progresses,atoms of the emitter 22 which are evaporated and floating due to theJoule heat are ionized into positive ions and electrons by the emittedelectrons, and the electrons produced by the ionization ionize atoms ofthe emitter 22. Therefore, the number of electrons is exponentiallyincreased. When such a process goes on, electrons and positive ions arepresent in a neutral fashion, developing a local plasma. Secondaryelectrons are also considered as promoting the ionization. The positiveions produced by the ionization may impinge upon the upper electrode 18,thus damaging the upper electrode 18.

As shown in FIG. 7, electrons drawn from the upper electrode 18 areattracted to the positive poles of dipole moments of the emitter 22which are present as a local anode, negatively charging the surface ofthe emitter 22 in the vicinity of the upper electrode 18. As a result,the factor for accelerating electrons (local potential difference) islessened, no potential is present for the emission of secondaryelectrons, and the surface of the emitter 22 is further negativelycharged.

Therefore, the positive polarity of the local anode provided by thedipole moments is reduced, and the intensity E_(A) of the electric fieldbetween a local anode and a local cathode is reduced (in FIG. 7, areduction in the intensity E_(A) of the electric field is indicated bythe broken-line arrow), stopping the emission of electrons.

Specifically, as shown in FIG. 9A, when the drive voltage Va is appliedbetween the upper electrode 18 and the lower electrode 20 such that thevoltage Va1 is +100 V and the voltage Va2 is −100 V, for example, avoltage change ΔVak that occurs between the upper electrode 18 and thelower electrode 20 at a peak time point P1 when electrons are emitted iswithin 20 V (about 10 V in FIG. 9B), and hence the voltage Va issubstantially free of changes. Therefore, almost no positive ions areproduced, and the upper electrode 18 is prevented from being damaged bypositive ions, resulting in a longer service life of the electronemitter 12A.

The dielectric breakdown voltage of the emitter 22 should preferably beat least 10 kV/mm. In the present embodiment, if the thickness d of theemitter 22 is of 20 μm, for example, the emitter 22 will not sufferdielectric breakdown even when a drive voltage of −100 V is appliedbetween the upper electrode 18 and the lower electrode 20.

When electrons emitted from the emitter 22 impinge again upon theemitter 22 or atoms are ionized in the vicinity of the surface of theemitter 22, the emitter 22 may possibly be damaged, inducing crystaldefects and resulting in a fragile structure.

The emitter 22 should preferably be made of a dielectric material havinga high evaporation temperature in vacuum, e.g., BaTiO₃ containing no Pbor the like. The atoms of the emitter 22 thus formed are less likely toevaporate due to the Joule heat, and are prevented from being ionized byelectrons. This approach is effective in protecting the surface of theemitter 22.

The pattern shape and potential of the collector electrode 32 mayappropriately be changed and unillustrated control electrodes or thelike may be disposed between the emitter 22 and the collector electrode32 to establish a desired electric field distribution between theemitter 22 and the collector electrode 32, thereby controlling thetrajectory of emitted secondary electrons and converging, enlarging, andmodifying the electron beam diameter with ease.

Since the electron emitters 12A output secondary electrons emitted fromthe emitter 22, the service life and reliability thereof for electronemission can be increased. Furthermore, as the electron emitters 12A arearranged in a two-dimensional array in the first embodiment, there isrealized a planar light source which can be of a longer service life andof increased reliability.

Advantages of planar light sources will be described below in terms oftheir differences with displays. Unlike a display, a planar light sourcemay emit light from its entire surface at all times, and hence does notneed to be driven under complex control such as row scanning control,etc., but may be driven altogether statically. Since the diameter of alight emission spot produced by an electron emission does not need to becontrolled, it is not necessary to install a control electrode, etc.functioning as a focusing lens, for example, between the electronemitters and the phosphors. This leads to a simplified mechanicalarrangement and a simplified circuit arrangement.

The display needs to handle a data signal that changes at a high speeddepending on the pixel signal. Therefore, the drive voltage is of acomplex waveform that is modulated depending on the gradation. On theother hand, as the planar light source is not required to handle a datasignal that changes at a high speed depending on the pixel signal, thedrive voltage may be of a simple waveform, i.e., a waveform having aconstant pulse period or pulse duration. As a result, if an electricpower retrieval circuit, to be described later, is connected to theplanar light source, not only the circuit constants, circuit switchingtiming, etc. of the electric power retrieval circuit can be set withhigh accuracy, but also almost 100% of the drive voltage can beretrieved.

In the above embodiment, the collector electrode 32 is disposed on thereverse side of the transparent panel 30, and the phosphor 34 isdisposed on the surface of the collector electrode 32 which faces theupper electrode 18. In a light source 10Aa according to a firstmodification shown in FIG. 10, phosphors 34 are disposed on the reverseside of the transparent panel 30, and the collector electrode 32 isdisposed in covering relation to the phosphors 34. In this case, thecollector electrode 32 functions as a metal back. Secondary electronsemitted from the emitter 22 pass through the collector electrode 32 intothe phosphors 34, exciting the phosphors 34. Therefore, the collectorelectrode 32 is of a thickness which allows electrons to passtherethrough, preferably 100 nm or less. As the kinetic energy of thesecondary electrons is larger, the thickness of the collector electrode32 may be increased.

This arrangement offers the following advantages:

(1) If the phosphor 34 is not electrically conductive, then the phosphor34 is prevented from being charged (negatively), and an electric fieldfor accelerating electrons can be maintained.

(2) The collector electrode 32 reflects light emitted from the phosphor34, and discharges the light emitted from the phosphor 34 efficientlytoward the transparent panel 30 (light emission surface).

(3) Secondary electrons are prevented from impinging excessively uponthe phosphor 34, thus preventing the phosphor 34 from being deterioratedand from producing a gas.

FIG. 11 shows a light source 10Ab according to a second modification. Inthe light source 10Ab, the phosphor 34 is formed on the transparentpanel 30, and mercury particles 40, for example, are sealed in theatmosphere between the light emitting section 14A having the electronemitters 12A and the phosphor 34. In this case, some of secondaryelectrons emitted from the electron emitters 12A impinge upon themercury particles 40, which are excited to emit ultraviolet rays 42. Theultraviolet rays 42 hit the phosphor 34, which is excited to emitfluorescent light.

As shown in FIG. 12, the drive circuit 16A comprises a timing generatingcircuit 44 and a drive voltage generating circuit 46.

The timing generating circuit 44 generates and outputs a timing pulse Ptfor determining the output timing of the drive pulse Pd based on thecontrol signal Sc representative of turn-on/turn-off and a clock signalPc. Specifically, as shown in FIG. 13A, the timing generating circuit 44starts counting the clock signal Pc (see FIG. 13B) from the time whenthe control signal Sc goes high (a level representative of turn-on). Asshown in FIG. 13C, the timing generating circuit 44 repeatedly generatesand outputs a high-level timing pulse Pt during a period T2corresponding to m clock pulses and a low-level timing pulse Pt during aperiod T2 corresponding to n clock pulses. The timing pulses Pt aresuccessively output only during a period (turn-on period Ts) in whichthe control signal Sc represents turn-on. During a period in which thecontrol signal Sc is of a low level (a level representative ofturn-off), i.e., during a turn-off period Tn, the timing generatingcircuit 44 outputs only a low-level signal.

The drive voltage generating circuit 46 generates and outputs a drivevoltage Va to be applied between the upper electrode 18 and the lowerelectrode 20 of each of the electron emitters 12A based on the timingpulses Pt from the timing generating circuit 44. Specifically, as shownin FIG. 13D, the drive voltage generating circuit 46 outputs a voltageVa1 during the period T1, in which the output level of the timinggenerating circuit 44 is low, and outputs a voltage Va2 during theperiod T2, in which the output level of the timing generating circuit 44is high. Therefore, the drive voltage Va output from the drive voltagegenerating circuit 46 has a waveform representing a succession of drivepulses Pd in synchronism with the timing pulses Pt from the timinggenerating circuit 44.

During the turn-on period Ts, each of the electron emitters 12Acontinuously emits electrons to excite the phosphor 34 in response tothe application of drive pulses Pd between the upper electrode 18 andthe lower electrode 20 of the electron emitter 12A. As a result, thefluorescent light emission is sustained during the turn-on period Ts.During the turn-off period Tn, since no drive pulses Pd are appliedbetween the upper electrode 18 and the lower electrode 20 of each of theelectron emitters 12A, the emission of electrons from the electronemitter 12A are stopped, keeping the light source turned off until anext turn-on instruction.

A preferred embodiment of the drive circuit 16A will be described belowwith reference to FIGS. 14 and 15. The drive circuit 16A according tothe present embodiment has, as shown in FIG. 14, the timing generatingcircuit 44 and the drive voltage generating circuit 46 as describedabove, and an electric power retrieval circuit 50. In FIG. 14, all theelectron emitters 12A in the light emitting section 14A are representedas a single capacitor C. One of the electrodes of the capacitor Crepresents the upper electrodes 18 of all the electron emitters 12A, andthe other of the electrodes of the capacitor C represents the lowerelectrodes 20 of all the electron emitters 12A.

A conceptual arrangement of the electric power retrieval circuit 50 willbe described below. A buffer capacitor Cf and a first series-connectedcircuit 52 are connected parallel to each other between both electrodes(the upper electrode 18 and the lower electrode 20) of the capacitor C.A second series-connected circuit 54 is also connected between thecapacitor C and the buffer capacitor Cf.

In the embodiment shown in FIG. 14, one buffer capacitor Cf is connectedto one capacitor C. However, two or more buffer capacitors Cf may beconnected to one capacitor C, and the number of buffer capacitors Cf isarbitrary.

The first series-connected circuit 52 comprises a first switchingcircuit SW1, a current-suppressing first resistor r, and a positivepower supply 56 (voltage Va1) which are connected in series to eachother. The second series-connected circuit 54 comprises a secondswitching circuit SW2 and an inductor 58 (inductance L) which areconnected in series to each other.

The drive voltage generating circuit 46 generates and outputs controlsignals Sc1, Sc2 for controlling the first switching circuit SW1 and thesecond switching circuit SW2 based on timing pulses Pt from the timinggenerating circuit 44.

Operation of the drive circuit 16A according to the present embodimentwill be described with reference to FIG. 15.

Prior to the start of the turn-on period Ts, the first switching circuitSW1 is turned on and the second switching circuit SW2 is turned off. Thevoltage across the capacitor C is substantially the same as the voltageVa1 of the positive power supply 56.

In the turn-on period Ts, at time t1 when the period T2 starts, thefirst switching circuit SW1 is turned off and the second switchingcircuit SW2 is turned on by the drive voltage generating circuit 46. Theinductor 58 and the capacitor C start oscillating sinusoidally,whereupon the voltage across the capacitor C starts being attenuatedresonantly. At this time, electric charges stored in the capacitor C areretrieved by the buffer capacitor Cf.

At time t2, i.e., at the time when the oscillating waveform (voltagewaveform) of the capacitor C is of the lowest level (voltage:—Va1=Va2),the second switching circuit SW2 is turned off by the drive voltagegenerating circuit 46, placing the system of the capacitor C and thebuffer capacitor Cf in a high impedance state. From time t2 on, thevoltage Va2 is maintained until time t3 when the period T2 ends. Asdescribed above, when the voltage Va1 drops to the voltage Va2, theemitters 22 of the electron emitters 12A emit secondary electrons toemit light through the entire surface of the transparent panel 30.

Thereafter, at time t3 when the period T2 ends, the second switchingcircuit SW2 is turned on by the drive voltage generating circuit 46. Theinductor 62 and the capacitor C start oscillating sinusoidally,whereupon the voltage across the capacitor C starts being amplifiedresonantly. At this time, electric charges stored in the buffercapacitor Cf are charged in the capacitor C.

At time t4, i.e., at the time when the oscillating waveform (voltagewaveform) of the capacitor C is of the highest level (voltage: Va1), thesecond switching circuit SW2 is turned off and the first switchingcircuit SW1 is turned on by the drive voltage generating circuit 46.From time t4 on, the voltage Va1 is maintained until time t2 when thenext period T2 starts.

As shown in FIGS. 13A through 13D, one step of successive periods T2, T1is repeated during the turn-on period Ts. Even when the electron emitter12A self-inactivates the emission of electrons, since a next period T2comes to emit electrons, the emission of light is apparently maintainedthrough the entire surface of the transparent panel 30 throughout theperiod Ts. Specifically, before the light emitted by a single emissionof electrons is extinguished, a next emission of electrons occurs,causing the light source to emit light continuously.

In the turn-off period Tn, as shown in FIGS. 13A through 13D, since thevoltage Va1 is continuously applied to each of the electron emitters12A, no electrons are emitted from the electron emitters 12A, keepingthe light source turned off throughout the turn-off period Tn.

The electric power retrieval circuit 50 connected to the drive circuit16A makes it possible to retrieve almost 100% of the drive voltage Va,resulting in an advantage for the reduction of electric powerconsumption. In this embodiment, the first series-connected circuit 52is included to forcibly change the voltage across the capacitor C to thevoltage Va1 at a predetermined time. Therefore, an attenuation of thedrive voltage due to the electric power consumption by the inductor 58can be avoided. At the time of starting to use the light source 10A, thevoltage across the capacitor C may be set to the voltage Va1, andthereafter the capacitor C and the buffer capacitor Cf may alternatelybe charged and discharged only by turning on and off the secondswitching circuit SW2.

With the light source 10A according to the first embodiment, the drivevoltage Va is applied to the upper and lower electrodes 18, 20 of allthe electron emitters 12A to cause the light emitting section 14A toemit light through the entire surface of the transparent panel 30. Witha light source 10Ac according to a third modification shown in FIG. 16,the light emitting section 14A is divided into two groups (first andsecond groups G1, G2). When the electron emitters 12A in the group G1emit light, the electron emitters 12A in the group G2 retrieve electricpower of the electron emitters 12A in the group G1, and when theelectron emitters 12A in the group G2 emit light, the electron emitters12A in the group G1 retrieve electric power of the electron emitters 12Ain the group G2.

If the electron emitters 12A in the group G1 are represented as acapacitor C1 and the electron emitters 12A in the group G2 by acapacitor C2, then the drive circuit 16A may include the capacitor C1instead of the capacitor C and the capacitor C2 instead of the buffercapacitor Cf as indicated by the parentheses in FIG. 14.

Operation of the drive circuit 16A as applied to the light source 10Acwill be described below with reference to FIG. 17. Prior to the start ofthe turn-on period Ts, the first switching circuit SW1 is turned on andthe second switching circuit SW2 is turned off. The voltage across thecapacitor C is substantially the same as the voltage Va1 of the positivepower supply 56.

In the turn-on period Ts, at time t1 when the period T2 starts, thefirst switching circuit SW1 is turned off and the second switchingcircuit SW2 is turned on by the drive voltage generating circuit 46. Theinductor 58 and the capacitor C1 start oscillating sinusoidally,whereupon the voltage across the capacitor C1 starts being attenuatedresonantly. At this time, electric charges stored in the capacitor C1are retrieved by the buffer capacitor Cf.

Specifically, as viewed from the capacitor C2, the inductor 58 and thecapacitor C1 start oscillating sinusoidally at time t1, and the voltageacross the capacitor C2 starts being amplified resonantly. At this time,electric charges stored in the capacitor C1 are retrieved by thecapacitor C2.

At time t2, i.e., at the time when the oscillating waveform (voltagewaveform) of the capacitor C1 is of the lowest level (voltage:—Va1=Va2),the second switching circuit SW2 is turned off by the drive voltagegenerating circuit 46, placing the system of the capacitor C1 and thecapacitor C2 in a high impedance state. From time t2 on, the capacitorC1 maintains the voltage Va2 and the capacitor C2 maintains the voltageVa1 until time t3 when the period T2 ends.

Particularly, since the voltage across the capacitor C1 quickly dropsfrom the voltage Va1 to the voltage Va2 from time t1 to time t2, theemitters 22 of the electron emitters 12A in the group G1 as shown inFIG. 16 emit secondary electrons. Because of the emission of thesecondary electrons, the light source 10Ac emits light through theregion of the transparent panel 30 which corresponds to the first groupG1.

The period T2 is a period for emitting electrons from the capacitor C1,and is also a preparatory period T1 until the emission of electrons asviewed from the capacitor C2. Therefore, the period T1 should preferablybe equal to the period T2.

Thereafter, at time t3 when the period T2 ends, the second switchingcircuit SW2 is turned on by the drive voltage generating circuit 46. Theinductor 62 and the capacitor C1 start oscillating sinusoidally,whereupon the voltage across the capacitor C starts being amplifiedresonantly. At this time, electric charges stored in the capacitor C2are charged in the capacitor C1.

Specifically, as viewed from the capacitor C2, the inductor 58 and thecapacitor C2 start oscillating sinusoidally at time t3, and the voltageacross the capacitor C2 starts being attenuated resonantly. At thistime, electric charges stored in the capacitor C2 are retrieved by thecapacitor C1.

At time t4, i.e., at the time when the oscillating waveform (voltagewaveform) of the capacitor C1 is of the highest level (voltage: Va1),the second switching circuit SW2 is turned off and the first switchingcircuit SW1 is turned on by the drive voltage generating circuit 46.From time t4 on, the capacitor C1 maintains the voltage Va1 and thecapacitor C2 maintains the voltage Va2 until time t2 when the nextperiod T2 starts.

Since the voltage across the capacitor C2 quickly drops from the voltageVa1 to the voltage Va2 from time t3 to time t4, the emitters 22 of theelectron emitters 12A in the group G2 as shown in FIG. 16 emit secondaryelectrons. Because of the emission of the secondary electrons, the lightsource 10Ac emits light through the region of the transparent panel 30which corresponds to the second group G2.

The period T1 starts from time t3. The period T1 is a period foremitting electrons from the capacitor C1, and is also the period T2 foremitting electrons as viewed from the capacitor C2.

A succession of periods T2, T1 (one step) is repeated during the turn-onperiod Ts to emit electrons alternately from the electron emitters 12Ain the group G1 and the electron emitters 12A in the group G2.Therefore, by appropriately setting the period T1 or T2, the lightsource 10Ac apparently maintains light emission through the entiresurface of the transparent panel 30 throughout the turn-on period Ts. Itis also possible to intentionally increase the period T1 or the periodT2 to allow human eyes to distinguish the emission of light from thefirst group G1 from the emission of light from the second group G2.

With the light source 10Ac according to the third modification, theelectron emitters 12A in the group other than the group which isemitting light double as a buffer capacitor Cf for retrieving electricpower. Therefore, no separate buffer capacitor Cf is required, and hencethe light source 10Ac may be mounted in a reduced area and may consumereduced electric power. The electron emitter 12A in the first group G1and the electron emitter 12A in the second group G2 may be positioned inscattered units for achieving apparent uniform planar light emission atall times.

In the above embodiments, each of the electron emitters 12A emits aconstant quantity of electrons. FIG. 18 shows a drive circuit 16Aaaccording to a modification, which comprises the timing generatingcircuit 44, the drive voltage generating circuit 46, and a modulationcircuit 60. The modulation circuit 60 is a circuit for controlling thequantity of electrons emitted from each of the electron emitters 12Adepending on a light control signal Sh from a light control volume (notshown) disposed outside of the drive circuit 16Aa.

The modulation circuit 60 may operate according to four modulationprocesses. The first modulation process modulates the pulse duration ofthe voltage Va2, as shown in FIG. 19B or 19C, based on the level(voltage level or the like) of the light control signal Sh, as shown inFIG. 19A. As shown in FIG. 19B, the period T2 itself may be modulated,or as shown in FIG. 19C, the period T2 may be constant, and the periodTa in which to apply the voltage Va2 may be modulated. The modulationprocess shown in FIG. 19C is based on the fact that the pulse durationof the voltage Va2 and luminance are linearly related to each other asshown in FIG. 20. For example, the luminance can be changed from 0 toabout 1020 (cd/m²) by varying the pulse duration from 0 to about 600μsec. Since the pulse duration of the voltage Va2 may be controlled,highly fine gradation representations can be achieved by performing aninexpensive digital control process.

The second modulation process is a process of controlling the collectorvoltage Vc, and is based on the fact that the collector voltage Vc andluminance are linearly related to each other as shown in FIG. 21. Forexample, if the collector voltage Vc is varied from 4 kV to 7 kV, thenthe luminance can be changed from 0 to 600 (cd/m²).

The third modulation process is a process of controlling the voltage Va2(voltage level) of the drive voltage V1, and is based on the fact thatthe voltage Va2 and luminance are linearly related to each other asshown in FIG. 22. For example, the luminance can be changed from 0 to1600 (cd/m²) by varying the voltage Va2 from about 118 V to 188 V.

The fourth modulation process is a process of controlling the voltageVa1 of the drive voltage Va. Since the voltage Va1 and luminance arenonlinearly related to each other as shown in FIG. 23. Therefore, it isdifficult to control the voltage Va1, and some circuit refinement isneeded as analog voltage control over the voltage Va1 is necessary.

Of the first through fourth modulation processes, therefore, it ispreferable to adopt the first modulation process for modulating thepulse duration of the voltage Va2.

As shown in FIG. 1, the light source 10A according to the firstembodiment has one collector electrode 32 associated with a plurality ofelectron emitters 12A, and a bias voltage Vc is applied to the collectorelectrode 32 through the resistor R2. However, a light source 10Adaccording to a fourth modification shown in FIG. 24 has as manycollector electrodes 32(1), 32(2), . . . , 32(N) as the number ofcolumns of the light source 10Ad, and resistors Rc1, Rc2, . . . , RcNconnected respectively to the collector electrodes 32(1), 32(2), . . . ,32(N). With this arrangement, variations introduced in the manufacturingprocess, e.g., luminance variations of the electron emitters 12A, may beadjusted by the resistors Rc1, Rc2, . . . , RcN connected respectivelyto the collector electrodes 32(1), 32(2), 32(N).

Adjustment of luminance variations will be described below withreference to FIGS. 25 through 28.

According to a conventional process of lowering variations, as describedin the document: Kanemaru, Seigou, “Featuring: All About Flat Displays2000, Leading Technological Trend of FEDs,” Electronic Engineering,Nikkan Kogyo Shimbun, Ltd., July 2000, pp. 38-41, for example,current-suppressing resistors are connected to emitters for loweringvariations.

The conventional process is based on the relationship between thecurrent flowing through the emitter and the gate voltage, and requires anumber of simulations to be performed until optimum resistances forlowering luminance variations are obtained.

According to the present embodiment, there is employed a process ofadjusting the electric field between the collector electrode 32 that isactually reached by emitted electrons and the upper electrode 18, fordirectly adjusting luminance variations to lower the luminancevariations quickly with accuracy.

The process of lowering luminance variations according to the presentembodiment will specifically be described below. As shown in FIG. 25, aresistor Rk connected between the upper electrode 18 and a negativepower supply 70 which applies a negative voltage Vk (e.g., a voltagewhich is the same as the voltage Va2 described above) between the upperelectrode 18 and the lower electrode 20, and a resistor Rc connectedbetween the collector electrode 32 and a bias power supply 36 (biasvoltage Vc) are adjusted. As shown in FIG. 25, Rkc represents a resistoracross the gap between the upper electrode 18 and the collectorelectrode 32, Vkc a voltage across the gap, C a capacitance between theupper electrode 18 and the lower electrode 20, and Vak a voltage betweenthe upper electrode 18 and the lower electrode 20.

It is assumed that there are two electron emitters 12A(1), 12A(2). Whenthese electron emitters 12A(1), 12A(2) have different outputcharacteristics (Vkc vs. Ikc characteristics) as shown in FIG. 27, if itwere not for the resistors Rk, Rc, a current change in the electronemitters 12A(1), 12A(2) is represented by ΔI₁.

The current change ΔI₁ can be reduced to a current change ΔI₂ on a loadline 80 by connecting the resistors Rk, Rc.

The load line 80 can be drawn as follows: Based on the structure shownin FIG. 25, an equivalent circuit primarily in terms of a current Ikcflowing between the upper electrode 18 and the lower electrode 20 isplotted as shown in FIG. 26.

From the equivalent circuit, there is derived the following equation:Ikc=(Vk+Vc)/(Rc+Rkc+Rk)

Since the current Ikc is maximum when Rkc=0, the load line 80 is drawnas a line interconnecting a point Pa on the vertical axis shown in FIG.27 which represents Ikc=(Vk+Vc)/(Rc+Rk) and a point Pb on the horizontalaxis which represents Vkc=Vk+Vc.

As Rc+Rk is greater, the current Ikc becomes smaller, reducing luminancevariations between the electron emitters 12A(1), 12A(2).

If a control electrode (not shown) is connected between the upperelectrode 18 and the collector electrode 32, then an equivalent circuitprimarily in terms of a collector current Ic flowing through thecollector electrode 32 and a control current Ig flowing through thecontrol electrode is plotted as shown in FIG. 28. A resistor Rg isconnected between the control electrode and a negative power supply 72which applies a negative voltage Vg between the control electrode andthe lower electrode 20. In FIG. 28, Rkg represents a resistor across thegap between the upper electrode 18 and the control electrode. Thecollector current Ic is 60% of a cathode current Ik, and the controlcurrent Ig is 40% of the cathode current Ik.

From the equivalent circuit shown in FIG. 28, there is derived thefollowing equation:Ig=(Vg+Vk)/(Rg+Rkg+Rk)

Based on the above equation, a load line is drawn, and the voltage Vgand the resistor Rg for minimizing luminance variations are determined.With the voltage Vg and the resistor Rg determined, the control currentIg and the cathode current Ik are determined, and so is the collectorcurrent Ic of necessity.

As shown in FIG. 1, the light source 10A according to the firstembodiment has a single light emitting section 14A including all theelectron emitters 12A, and a single drive circuit 16A connected to thelight emitting section 14A. A light source 10Ae according to a fifthmodification shown in FIG. 29 has two or more planar light sourcesections Z1 through Z6. In the fifth modification shown in FIG. 29, thelight source 10Ae has six planar light source sections Z1 through Z6.Each of the planar light source sections Z1 through Z6 has atwo-dimensional array of electron emitters 12A, and drive circuits 16Aare independently connected to the respective planar light sourcesections Z1 through Z6.

Each of the planar light source sections Z1 through Z6 can be controlledfor energization/de-energization. Particularly, if the drive circuits16A independently connected respectively to the planar light sourcesections Z1 through Z6 have modulation circuits 60 (see FIG. 18), thenthe light emission distributions of the planar light source sections Z1through Z6 can independently be controlled. That is, the light source10Ae can perform analog light control as well as digital light controlfor fine light control applications.

In the modification shown in FIG. 29, the planar light source sectionsZ1 through Z6 have equal areas. However, the planar light sourcesections Z1 through Z6 may have different areas. For example, FIG. 30shows a light source 10Af according to a sixth modification whichincludes first and sixth planar light source sections Z1, Z6 which areof a horizontally long rectangular shape with long sides, second andfifth planar light source sections Z2, Z5 which are of a vertically longrectangular shape with long sides shorter than the long sides of thefirst and sixth planar light source sections Z1, Z6, and third andfourth planar light source sections Z3, Z4 which are of a horizontallylong rectangular shape with long sides shorter than the long sides ofthe first and sixth planar light source sections Z1, Z6.

FIG. 31 shows a light source 10Ag according to a seventh modification.The light source 10Ag has first through sixth light source sections Z1through Z6. The electron emitters 12A in each of the first through sixthlight source sections Z1 through Z6 are divided into two groups (firstand second groups G1, G2). In each of the first through sixth lightsource sections Z1 through Z6, when the electron emitters 12A in thegroup G1 emit light, the electron emitters 12A in the group G2 retrieveelectric power of the electron emitters 12A in the group G1, and whenthe electron emitters 12A in the group G2 emit light, the electronemitters 12A in the group G1 retrieve electric power of the electronemitters 12A in the group G2.

FIG. 32 shows a light source 10Ah according to an eighth modification.The light source 10Ah has first through sixth light source sections Z1through Z6. The first through sixth light source sections Z1 through Z6are divided into two groups (first and second groups G1, G2). When theelectron emitters 12A in the planar light source sections Z1 through Z3in the group G1 emit light, the electron emitters 12A in the planarlight source sections Z4 through Z6 in the group G2 retrieve electricpower of the electron emitters 12A in the group G1, and when theelectron emitters 12A in the planar light source sections Z4 through Z6in the group G2 emit light, the electron emitters 12A in the planarlight source sections Z1 through Z3 in the group G1 retrieve electricpower of the electron emitters 12A in the group G2.

With the light sources 10Ae through 10Ah according to the fifth througheighth modifications, the light emitting section 14A is divided into thesix planar light source sections Z1 through Z6. However, the number ofplanar light source sections is optional.

As shown in FIG. 1, the light source 10A according to the firstembodiment has a plurality of independent upper electrodes 18 disposedon the face side of one emitter 22, and a plurality of lower electrodes20 disposed independently on the reverse side of the emitter 22, thusproviding a plurality of electron emitters 12A. Other embodiments willbe described below with reference to FIGS. 33 trough 37. In FIGS. 33through 37, the collector electrode 32 and the phosphors 34 are omittedfrom illustration.

FIG. 33 shows a light source 10A according to a ninth modification. Thelight source 10A has a plurality of independent upper electrodes 18disposed on the face side of one emitter 22, and a single lowerelectrode 20 (common lower electrode) disposed on the reverse side ofthe emitter 22, thus providing a plurality of electron emitters 12A.

FIG. 34 shows a light source 10Aj according to a tenth modification. Thelight source 10Aj has a single very thin upper electrode 18 (commonupper electrode) having a thickness up to 10 nm, disposed on the faceside of one emitter 22, and a plurality of independent lower electrodes20 disposed on the reverse side of the emitter 22, thus providing aplurality of electron emitters 12A.

FIG. 35 shows a light source 10Ak according to an eleventh modification.The light source 10Ak has a plurality of lower electrodes 20 disposedindependently on a substrate 90, a single emitter 22 disposed incovering relation to the lower electrodes 20, and a plurality ofindependent upper electrodes 18 disposed on the emitter 22, thusproviding a plurality of electron emitters 12A. The upper electrodes 18are positioned above the corresponding lower electrodes 20 with theemitter 22 sandwiched therebetween.

FIG. 36 shows a light source 10Al according to a twelfth modification.The light source 10Al has a single lower electrode 20 disposed on asubstrate 90, a single emitter 22 disposed in covering relation to thelower electrode 20, and a plurality of independent upper electrodes 18disposed on the emitter 22, thus providing a plurality of electronemitters 12A.

FIG. 37 shows a light source 10Am according to a thirteenthmodification. The light source 10Am has a plurality of lower electrodes20 disposed independently on a substrate 90, a single emitter 22disposed in covering relation to the lower electrodes 20, and a singlevery thin upper electrode 18 disposed on the emitter 22, thus providinga plurality of electron emitters 12A.

A light source 10B according to a second embodiment of the presentinvention will be described below with reference to FIGS. 38 through 77.Those parts of the light source 10B according to the second embodimentwhich are identical or correspond to those of the light source 10Aaccording to the first embodiment are denoted by identical orcorresponding reference characters, and will not be described in detailbelow.

As shown in FIG. 38, each of electron emitters 12B of the light source10B according to the second embodiment comprises an emitter 22, an upperelectrode 18, a lower electrode 20, and a pulse generating source 100for applying a drive voltage Va between the upper electrode 18 and thelower electrode 20.

The upper electrode 18 has a plurality of through regions 102 where theemitter 22 is exposed. The emitter 22 has surface irregularities 104 dueto the grain boundary of a dielectric material that the emitter 22 ismade of. The through regions 102 of the upper electrode 18 are formed inareas corresponding to concavities 106 due to the grain boundary of thedielectric material. In the embodiment shown in FIG. 38, one throughregion 102 is formed in association with one concavity 106. However, onethrough region 102 may be formed in association with a plurality ofconcavities 106. The particle diameter of the dielectric material of theemitter 22 should preferably be in the range from 0.1 μm to 10 μm, andmore preferably be in the range from 2 μm to 7 μm. In the embodimentshown in FIG. 38, the particle diameter of the dielectric material is of3 μm.

In this embodiment, as shown in FIG. 39, each of the through regions 102of the upper electrode 18 has a peripheral portion 108 having a surface108 a facing the emitter 22, the surface 108 a being spaced from theemitter 22. Specifically, a gap 110 is formed between the surface 108 a,facing the emitter 22, of the peripheral portion 108 of the throughregion 102 and the emitter 22, and the peripheral portion 108 of thethrough region 102 of the upper electrode 18 is formed as an overhangingportion (flange). In the description which follows, “the peripheralportion 108 of the through region 102 of the upper electrode 18” isreferred to as “the overhanging portion 108 of the upper electrode 18”.In FIGS. 38, 39, 41A, 41B, 42A, 42B, 44, 46 through 49, and 54,convexities 112 of the surface irregularities 104 of the grain boundaryof the dielectric material are shown as having a semicircularcross-sectional shape. However, the convexities 112 are not limited tothe semicircular cross-sectional shape.

With the electron emitter 12B, the upper electrode 18 has a thickness tin the range of 0.01 μt≦10 μm, and the maximum angle θ between the uppersurface of the emitter 22, i.e., the surface of the convexity 112 (whichis also the inner wall surface of the concavity 106) of the grainboundary of the dielectric material, and the lower surface 108 a of theoverhanging portion 108 of the upper electrode 18 is in the range of1°≦θ≦60°. The maximum distance d in the vertical direction between thesurface of the convexity 112 (the inner wall surface of the concavity106) of the grain boundary of the dielectric material and the lowersurface 108 a of the overhanging portion 108 of the upper electrode 18is in the range of 0 μm<d≦10 μm.

In the electron emitter 12B, the shape of the through region 102,particularly the shape as seen from above, as shown in FIG. 40, is theshape of a hole 114, which may be a circular shape, an elliptical shape,a track shape, a shape including a curve, or a polygonal shape such as aquadrangular shape or a triangular shape. In FIG. 40, the shape of thehole 114 is a circular shape.

The hole 114 has an average diameter ranging from 0.1 μm to 10 μm. Theaverage diameter represents the average of the lengths of a plurality ofdifferent line segments passing through the center of the hole 114.

The materials of the emitter 22 are the same as those according to thefirst embodiment, and will not be described below.

The emitter 22 may be made by any of various thick-film formingprocesses including screen printing, dipping, coating, electrophoresis,aerosol deposition, etc., or any of various thin-film forming processesincluding an ion beam process, sputtering, vacuum evaporation, ionplating, chemical vapor deposition (CVD), plating, etc. Particularly, itis preferable to form a powdery piezoelectric/electrostrictive materialas the emitter 22 and impregnate the emitter 22 thus formed with glassof a low melting point or sol particles. According to this process, itis possible to form a film at a low temperature of 700° C. or lower or600° C. or lower.

The upper electrode 18 is made of an organic metal paste which canproduce a thin film after being baked. For example, a platinum resinatepaste or the like, should preferably be used. An oxide electrode forsuppressing a polarization inversion fatigue, which is made of rutheniumoxide (RuO₂), iridium oxide (IrO₂), strontium ruthenate (SrRuO₃),La_(1-x)Sr_(x)CoO₃ (e.g., x=0.3 or 0.5), La_(1-x)Ca_(x)MnO₃, (e.g.,x=0.2), La_(1-x)Ca_(x)Mn_(1-y)CO_(y)O₃ (e.g., x=0.2, y=0.05), or amixture of any one of these compounds and a platinum resinate paste, forexample, is preferable.

As shown in FIGS. 41A and 41B, the upper electrode 18 may preferably bein the form of a cluster 118 of a plurality of scale-like members 116(e.g., of graphite). Alternatively, as shown in FIGS. 42A and 42B, theupper electrode 18 may preferably be in the form of a cluster 122 ofelectrically conductive members 120 including scale-like members 116.The cluster 118 or 122 does not fully cover the surface of the emitter22, but a plurality of through regions 102 are provided through whichthe emitter 22 is partly exposed, and those portions of the emitter 22which face the through regions 102 serve as electron emission regions.

The upper electrode 18 may be made of any of the above materials by anyof thick-film forming processes including screen printing, spraycoating, coating, dipping, electrophoresis, etc., or any of variousthin-film forming processes including sputtering, an ion beam process,vacuum evaporation, ion plating, chemical vapor deposition (CVD),plating, etc. Preferably, the upper electrode 18 is made by any of theabove thick-film forming processes.

The lower electrode 20 is made of an electrically conductive material,e.g., a metal such as platinum, molybdenum, tungsten, or the like.Alternatively, the lower electrode 20 is made of an electric conductorwhich is resistant to a high-temperature oxidizing atmosphere, e.g., ametal, an alloy, a mixture of insulative ceramics and a metal, a mixtureof insulative ceramics and an alloy, or the like. Preferably, the lowerelectrode 20 should be made of a precious metal having a high meltingpoint such as platinum, iridium, palladium, rhodium, molybdenum, or thelike, or a material chiefly composed of an alloy of silver andpalladium, silver and platinum, platinum and palladium, or the like, ora cermet of platinum and ceramics. Further preferably, the lowerelectrode 20 should be made of platinum only or a material chieflycomposed of a platinum-base alloy.

The lower electrode 20 may be made of carbon or a graphite-basematerial. Ceramics to be added to the electrode material shouldpreferably have a proportion ranging from 5 to 30 volume %. The lowerelectrode 20 may be made of the same material as the upper electrode 18,as described above.

The lower electrode 20 should preferably be formed by any of variousthick-film forming processes. The lower electrode 20 has a thickness of20 μm or less or preferably a thickness of 5 μm or less.

Each time the emitter 22, the upper electrode 18, or the lower electrode20 is formed, the assembly is heated (sintered) into an integralstructure.

The sintering process for integrally combining the emitter 22, the upperelectrode 18, and the lower electrode 20 may be carried out at atemperature ranging from 500° to 1400° C., preferably from 1000° to1400° C. For heating the emitter 22 which is in the form of a film, theemitter 22 should be sintered together with its evaporation source whiletheir atmosphere is being controlled, so that the composition of theemitter 22 will not become unstable at high temperatures.

By performing the sintering process, the film which will serve as theupper electrode 18 is shrunk from the thickness of 10 μm to thethickness of 0.1 μm, and simultaneously a plurality of holes are formedtherein. As a result, as shown in FIG. 38, a plurality of throughregions 102 are formed in the upper electrode 18, and the peripheralportions 108 of the through regions 102 are turned into overhangingportions. In advance (of the sintering process), the film which willserve as the upper electrode 18 may be patterned by etching (wet etchingor dry etching) or lift-off, and then may be sintered. In this case,recesses or slits may easily be formed as the through regions 102.

The emitter 22 may be covered with a suitable member, and then sinteredsuch that the surface of the emitter 22 will not be exposed directly tothe sintering atmosphere.

The principles of electron emission of the electron emitter 12B will bedescribed below. First, a drive voltage Va is applied between the upperelectrode 18 and the lower electrode 20. The drive voltage Va is definedas a voltage, such as a pulse voltage or an alternating-current voltage,which abruptly changes with time from a voltage level that is higher orlower than a reference voltage (e.g., 0 V) to a voltage level that islower or higher than the reference voltage.

A triple junction is formed in a region of contact between the uppersurface of the emitter 22, the upper electrode 18, and a medium (e.g., avacuum) around the electron emitter 12B. The triple junction is definedas an electric field concentration region formed by a contact betweenthe upper electrode 18, the emitter 22, and the vacuum. The triplejunction includes a triple point where the upper electrode 18, theemitter 22, and the vacuum exist as one point. The vacuum level in theatmosphere should preferably in the range from 10² to 10⁻⁶ Pa and morepreferably in the range from 10⁻³ to 10⁻⁵ Pa.

According to the second embodiment, the triple junction is formed on theoverhanging portion 108 of the upper electrode 18 and the peripheralarea of the upper electrode 18. Therefore, when the above drive voltageVa is applied between the upper electrode 18 and the lower electrode 20,an electric field concentration occurs at the triple junction.

A first electron emission process for the electron emitter 12B will bedescribed below with reference to FIGS. 43 and 44. In a first outputperiod T1 (first stage) shown in FIG. 43, a voltage V2 lower than areference voltage (e.g., 0 V) is applied to the upper electrode 18, anda voltage V1 higher than the reference voltage is applied to the lowerelectrode 20. In the first output period T1, an electric fieldconcentration occurs at the triple junction referred to above, causingthe upper electrode 18 to emit primary electrons toward the emitter 22.The emitted electrons are accumulated in the portions of the emitter 22which are exposed through the through region 102 of the upper electrode18 and regions near the outer peripheral portion of the upper electrode18, thus charging the emitter 22. At this time, the upper electrode 18functions as an electron supply source.

In a next output period T2 (second stage), the voltage level of thedrive voltage Va abruptly changes, i.e., the voltage V1 higher than thereference voltage is applied to the upper electrode 18, and the voltageV2 lower than the reference voltage to the lower electrode 20. Theelectrons that have been accumulated in the portions of the emitter 22which are exposed through the through region 102 of the upper electrode18 and the regions near the outer peripheral portion of the upperelectrode 18 are expelled from the emitter 22 by dipoles (whose negativepoles appear on the surface of the emitter 22) in the emitter 22 whosepolarization has been inverted in the opposite direction. The electronsare emitted from the portions of the emitter 22 where the electrons havebeen accumulated, through the through regions 102. The electrons arealso emitted from the regions near the outer peripheral portion of theupper electrode 18.

A second electron emission process will be described below withreference to FIGS. 45 and 46. In a first output period T1 (first stage)shown in FIG. 45, a voltage V3 higher than the reference voltage isapplied to the upper electrode 18, and a voltage V4 lower than thereference voltage is applied to the lower electrode 20. In the firstoutput period T1, the electron emitter 12B is prepared for electronemission. In a next output period T2 (second stage), the voltage levelof the drive voltage Va abruptly changes, i.e., the voltage V4 lowerthan the reference voltage is applied to the upper electrode 18, and thevoltage V3 higher than the reference voltage to the lower electrode 20.An electric field concentration occurs at the triple junction referredto above, causing the upper electrode 18 to emit primary electrons,which impinge upon the portions of the emitter 22 which are exposedthrough the through region 102 and regions near the outer peripheralportion of the upper electrode 18. As shown in FIG. 46, secondaryelectrons (including reflected primary electrons) are emitted from theportions hit by the primary electrons. Thus, secondary electrons areemitted from the through region 102 and the regions near the outerperipheral portion of the upper electrode 18 in an initial state of thedrive period T2.

The electron emitter 12B offers the following advantages: Since theupper electrode 18 has the plural through regions 102, electrons areuniformly emitted from each of the through regions 102 and the outerperipheral portions of the upper electrode 18. Thus, any variations inthe overall electron emission characteristics of the electron emitter12B are reduced, making it possible to facilitate the control of theelectron emission and increase the electron emission efficiency.

Because the gap 110 is formed between the overhanging portion 108 of theupper electrode 18 and the emitter 22, when the drive voltage Va isapplied, an electric field concentration tends to be produced in theregion of the gap 110. This leads to a higher efficiency of the electronemission, making the drive voltage lower (emitting electrons at a lowervoltage level).

As described above, according to the second embodiment, since the upperelectrode 18 has the overhanging portion 108 on the peripheral portionof the through region 102, together with the increased electric fieldconcentration in the region of the gap 110, electrons are easily emittedfrom the overhanging portion 108 of the upper electrode 18. This leadsto a larger output and higher efficiency of the electron emission,making the drive voltage Va lower. The light source 10B according to thesecond embodiment, which has a number of arrayed electron emitters 12B,has a higher level of luminance.

According to either the first electron emission process (which emitselectrons accumulated in the emitter 22) or the second electron emissionprocess (which emits secondary electrons by forcing primary electronsfrom the upper electrode 18 into impingement upon the emitter 22), asthe overhanging portion 108 of the upper electrode 18 functions as agate electrode (a control electrode, a focusing electronic lens, or thelike), the straightness of emitted electrons can be increased. This iseffective in reducing crosstalk if a number of electron emitters 12B arearrayed for use as an electron source of displays.

As described above, the light source 10B according to the secondembodiment is capable of easily developing a high electric fieldconcentration, provides many electron emission regions, has a largeroutput and higher efficiency of the electron emission, and can be drivenat a lower voltage (lower power consumption).

According to the second embodiment in particular, at least the uppersurface of the emitter 22 has the surface irregularities 104 due to thegrain boundary of the dielectric material. As the upper electrode 18 hasthe through regions 102 in portions corresponding to the concavities 106of the grain boundary of the dielectric material, the overhangingportions 108 of the upper electrode 18 can easily be realized.

The maximum angle θ between the upper surface of the emitter 22, i.e.,the surface of the convexity 112 (which is also the inner wall surfaceof the concavity 106) of the grain boundary of the dielectric material,and the lower surface 108 a of the overhanging portion 108 of the upperelectrode 18 is in the range of 1°≦θ≦60°. The maximum distance d in thevertical direction between the surface of the convexity 112 (the innerwall surface of the concavity 106) of the grain boundary of thedielectric material and the lower surface 108 a of the overhangingportion 108 of the upper electrode 18 is in the range of 0 μm<d≦10 μm.These arrangements make it possible to increase the degree of theelectric field concentration in the region of the gap 110, resulting ina larger output and higher efficiency of the electron emission andmaking the drive voltage lower efficiently.

According to the second embodiment, the through region 102 is in theshape of the hole 114. As shown in FIG. 39, the portions of the emitter22 where the polarization is inverted or changed depending on the drivevoltage Va applied between the upper electrode 18 and the lowerelectrode 20 (see FIG. 38) include a portion (first portion) 124directly below the upper electrode 18 and a portion (second portion) 126corresponding to a region extending from the inner peripheral edge ofthe through region 102 inwardly of the through region 102. Particularly,the second portion 126 changes depending on the level of the drivevoltage Va and the degree of the electric field concentration. Accordingto the second embodiment, the average diameter of the hole 114 is in therange from 0.1 μm to 10 μm. Insofar as the average diameter of the hole114 is in this range, the distribution of electrons emitted through thethrough region 102 is almost free of any variations, allowing electronsto be emitted efficiently.

If the average diameter of the hole 114 is less than 0.1 μm, then theregion where electrons are accumulated is made narrower, reducing theamount of emitted electrons. While one solution would be to form manyholes 114, it would be difficult and highly costly to form many holes114. If the average diameter of the hole 114 is in excess of 10 μm, thenthe proportion (share) of the portion (second portion) 126 whichcontributes to the emission of electrons in the portion of the emitter22 that is exposed through the through region 102 is reduced, resultingin a reduction in the electron emission efficiency.

The overhanging portion 108 of the upper electrode 18 may have upper andlower surfaces extending horizontally as shown in FIG. 39.Alternatively, as shown in FIG. 47, the overhanging portion 108 may havea lower surface 108 a extending substantially horizontally and an upperend raised upwardly. Alternatively, as shown in FIG. 48, the overhangingportion 108 may have a lower surface 108 a inclined progressivelyupwardly toward the center of the through region 102. Furtheralternatively, as shown in FIG. 49, the overhanging portion 108 may havea lower surface 108 a inclined progressively downwardly toward thecenter of the through region 102. The arrangement shown in FIG. 47 iscapable of increasing the function as a gate electrode. The arrangementshown in FIG. 49 makes it easier to produce a higher electric fieldconcentration for a larger output and higher efficiency of the electronemission because the gap 110 is narrower.

As shown in FIG. 50, the electron emitter 12B according to the secondembodiment has in its electrical operation a capacitor C1 due to theemitter 22 and a cluster of capacitors Ca due to respective gaps 110,disposed between the upper electrode 18 and the lower electrode 20. Thecapacitors Ca due to the respective gaps 110 are connected parallel toeach other into a single capacitor C2. In terms of an equivalentcircuit, the capacitor C1 due to the emitter 22 is connected in seriesto the capacitor C2 which comprises the cluster of capacitors Ca.

Actually, the capacitor C1 due to the emitter 22 is not directlyconnected in series to the capacitor C2 which comprises the cluster ofcapacitors Ca, but the capacitive component that is connected in seriesvaries depending on the number of the through regions 102 formed in theupper electrode 18 and the overall area of the through regions 102.

Capacitance calculations will be performed on the assumption that 25% ofthe capacitor C1 due to the emitter 22 is connected in series to thecapacitor C2 which comprises the cluster of capacitors Ca, as shown inFIG. 51. Since the gaps 110 are in vacuum, the relative dielectricconstant thereof is 1. It is assumed that the maximum distance d acrossthe gaps 110 is 0.1 μm, the area S of each gap 110 is S=1 μm×1 μm, andthe number of the gaps 110 is 10,000. It is also assumed that theemitter 22 has a relative dielectric constant of 2000, the emitter 22has a thickness of 20 μm, and the confronting area of the upper andlower electrodes 18, 20 is 200 μm×200 μm. The capacitor C2 whichcomprises the cluster of capacitors Ca has a capacitance of 0.885 pF,and the capacitor C1 due to the emitter 22 has a capacitance of 35.4 pF.If the portion of the capacitor C1 due to the emitter 22 which isconnected in series to the capacitor C2 which comprises the cluster ofcapacitors Ca is 25% of the entire capacitor C1, then thatseries-connected portion has a capacitance (including the capacitance ofcapacitor C2 which comprises the cluster of capacitors Ca) of 0.805 pF,and the remaining portion has a capacitance of 26.6 pF.

Because the series-connected portion and the remaining portion areconnected parallel to each other, the overall capacitance is 27.5 pF.This capacitance is 78% of the capacitance 35.4 pF of the capacitor C1due to the emitter 22. Therefore, the overall capacitance is smallerthan the capacitance of the capacitor C1 due to the emitter 22.

Consequently, the capacitance of the cluster of capacitors Ca due to thegaps 110 is relatively small. Because of the voltage division betweenthe cluster of capacitors Ca and the capacitor C1 due to the emitter 22,almost the entire applied voltage Va is applied across the gaps 110,which are effective to produce a larger output of the electron emission.

Since the capacitor C2 which comprises the cluster of capacitors Ca isconnected in series to the capacitor C1 due to the emitter 22, theoverall capacitance is smaller than the capacitance of the capacitor C1due to the emitter 22. This is effective to provide such preferredcharacteristics that the electron emission is performed for a largeroutput and the overall power consumption is lower.

Three modifications of the electron emitter 12B of the light source 10Baccording to the second embodiment will be described below withreference to FIGS. 52 through 54.

As shown in FIG. 52, an electron emitter 12Ba according to a firstmodification differs from the above electron emitter 12B in that thethrough region 102 has a shape, particularly a shape viewed from above,in the form of a recess 128. As shown in FIG. 52, the recess 128 shouldpreferably be shaped such that a number of recesses 128 are successivelyformed into a comb-like recess 130. The comb-like recess 130 iseffective to reduce variations in the distribution of electrons emittedthrough the through region 102 for efficient electron emission.Particularly, it is preferable to have the average width of the recesses128 in the range from 0.1 μm to 10 μm. The average width represents theaverage of the lengths of a plurality of different line segmentsextending perpendicularly across the central line of the recess 128.

As shown in FIG. 53, an electron emitter 12Bb according to a secondmodification differs from the above electron emitter 12B in that thethrough region 102 has a shape, particularly a shape viewed from above,in the form of a slit 132. The slit 132 is defined as something having amajor axis (extending in a longitudinal direction) whose length is 10times or more as long as the minor axis (extending in a transversedirection) thereof. Those having a major axis (extending in alongitudinal direction) whose length is less than 10 times as long asthe minor axis (extending in a transverse direction) thereof are definedas holes 114 (see FIG. 40). The slit 132 includes a succession of holes114 in communication with each other. The slit 132 should preferablyhave an average width ranging from 0.1 μm to 10 μm for reducingvariations in the distribution of electrons emitted through the throughregion 102 for efficient electron emission. The average width representsthe average of the lengths of a plurality of different line segmentsextending perpendicularly across the central line of the slit 132.

As shown in FIG. 54, an electron emitter 12Bc according to a thirdmodification differs from the above electron emitter 12B in that afloating electrode 134 exists on the portion of the upper surface of theemitter 22 which corresponds to the through region 102, e.g., in theconcavity 106 due to the grain boundary of the dielectric material. Withthis arrangement, since the floating electrode 134 also functions as anelectron supply source, the electron emitter 12Bc can emit manyelectrons through the through region 102 in an electron emission stage(the second output period T2 (see FIG. 43) according to the firstelectron emission process described above). The electron emission fromthe floating electrode 134 may be attributed to an electric fieldconcentration at the triple junction of the floating electrode 134, thedielectric material, and the vacuum.

The characteristics of the electron emitter 12B of the light source 10Baccording to the second embodiment, particularly, the voltage vs. chargequantity characteristics (the voltage vs. polarization quantitycharacteristics) thereof will be described below.

The electron emitter 12B is characterized by an asymmetric hysteresiscurve based on the reference voltage=0 (V) in vacuum, as indicated bythe characteristics shown in FIG. 55.

The voltage vs. charge quantity characteristics will be described below.If a region from which electrons are emitted is defined as an electronemission region, then at a point p1 (initial state) where the referencevoltage is applied, almost no electrons are stored in the electronemission region. Thereafter, when a negative voltage is applied, theamount of positive charges of dipoles whose polarization is inverted inthe emitter 22 in the electron emission region increases, and electronsare emitted from the upper electrode 18 toward the electron emissionregion in the first stage, so that electrons are stored. When theabsolute value of the negative voltage increases, electrons areprogressively stored in the electron emission region until the amount ofpositive charges and the amount of electrons are held in equilibriumwith each other at a point p2 of the negative voltage. As the absolutevalue of the negative voltage further increases, the stored amount ofelectrons increases, making the amount of negative charges greater thanthe amount of positive charges. The accumulation of electrons issaturated at a point P3. The amount of negative charges is the sum ofthe amount of electrons remaining to be stored and the amount ofnegative charges of the dipoles whose polarization is inverted in theemitter 22.

As the absolute value of the negative voltage then decreases, and apositive voltage is applied in excess of the reference voltage,electrons start being emitted at a point p4 in the second stage. Whenthe positive voltage increases in a positive direction, the amount ofemitted electrons increases until the amount of positive charges and theamount of electrons are held in equilibrium with each other at a pointp5. At a point p6, almost all the stored electrons are emitted, bringingthe difference between the amount of positive charges and the amount ofnegative charges into substantial conformity with a value in the initialstate. That is, almost all stored electrons are eliminated, and only thenegative charges of dipoles whose polarization is inverted in theemitter 22 appear in the electron emission region.

The voltage vs. charge quantity characteristics have the followingfeatures:

-   -   (1) If the negative voltage at the point p2 where the amount of        positive charges and the amount of electrons are held in        equilibrium with each other is represented by V1 and the        positive voltage at the point p5 by V2, then these voltages        satisfy the following relationship:        |V1|<|V2|    -   (2) More specifically, the relationship is expressed as        1.5×|V1|<|V2|    -   (3) If the rate of change of the amount of positive charges and        the amount of electrons at the point p2 is represented by        ΔQ1/ΔV1 and the rate of change of the amount of positive charges        and the amount of electrons at the point p5 by ΔQ2/ΔV2, then        these rates satisfy the following relationship:        (ΔQ1/ΔV1)>(ΔQ2/ΔV2)    -   (4) If the voltage at which the accumulation of electrons is        saturated is represented by V3 and the voltage at which        electrons start being emitted by V4, then these voltages satisfy        the following relationship:        1≦|V4|/|V3|≦1.5

The characteristics shown in FIG. 55 will be described below in terms ofthe voltage vs. polarization quantity characteristics. It is assumedthat the emitter 22 is polarized in one direction, with dipoles havingnegative poles facing toward the upper surface of the emitter 22 (seeFIG. 56A).

At the point p1 (initial state) where the reference voltage (e.g., 0 V)is applied as shown in FIG. 55, since the negative poles of the dipolemoments face toward the upper surface of the emitter 22, as shown inFIG. 56A, almost no electrons are accumulated on the upper surface ofthe emitter 22.

Thereafter, when a negative voltage is applied and the absolute value ofthe negative voltage is increased, the polarization starts beinginverted substantially at the time the negative voltage exceeds anegative coercive voltage (see the point p2 in FIG. 55). All thepolarization is inverted at the point p3 shown in FIG. 55 (see FIG.56B). Because of the polarization inversion, an electric fieldconcentration occurs at the triple junction, and the upper electrode 18emits electrons toward the emitter 22 in the first stage, causingelectrons to be accumulated in the portion of the emitter 22 which isexposed through the through region 102 of the upper electrode 18 and theportion of the emitter 22 which is near the peripheral portion of theupper electrode 18 (see FIG. 56C). In particular, electrons are emitted(emitted inwardly) from the upper electrode 18 toward the portion of theemitter 22 which is exposed through the through region 102 of the upperelectrode 18. At the point p3 shown in FIG. 55, the accumulation ofelectrons is saturated.

Thereafter, when the absolute value of the negative voltage is reducedand a positive voltage is applied in excess of the reference voltage,the upper surface of the emitter 22 is kept charged up to a certainvoltage level (see FIG. 57A). As the level of the positive voltage isincreased, there is produced a region where the negative poles ofdipoles start facing the upper surface of the emitter 22 (see FIG. 57B)immediately prior to the point p4 in FIG. 55. When the level is furtherincreased, electrons start being emitted due to coulomb repulsive forcesposed by the negative poles of the dipoles after the point p4 in FIG. 55(see FIG. 57C). When the positive voltage is increased in the positivedirection, the amount of emitted electrons is increased. Substantiallyat the time the positive voltage exceeds the positive coercive voltage(the point p5), a region where the polarization is inverted again isincreased. At the point p6, almost all the accumulated electrons areemitted, and the amount of polarization at this time is essentially thesame as the amount of polarization in the initial state.

The characteristics of the electron emitter 12B has have the followingfeatures:

-   -   (A) If the negative coercive voltage is represented by v1 and        the positive coercive voltage by v2, then        |v1|<|v2|    -   (B) More specifically, 1.5×|v1|<|v2|    -   (C) If the rate of change of the polarization at the time the        negative coercive voltage v1 is applied is represented by        Δq1/Δv1 and the rate of change of the amount of positive charges        and the rate of change of the polarization at the time the        positive coercive voltage v2 is applied is represented by        Δq2/Δv2, then        (Δq1/Δv1)>(Δq2/Δv2)    -   (D) If the voltage at which the accumulation of electrons is        saturated is represented by v3 and the voltage at which        electrons start being emitted by v4, then        1≦|v4|/|v3|≦1.5

Since the electron emitter 12B has the above characteristics, it caneasily be applied to the light source 10B according to the secondembodiment which has a plurality of electron emitters 12B arrayed inassociation with a plurality of pixels, for emitting light due to theemission of electrons from the electron emitters 12B.

The light source 10B which employs the electron emitters 12B will bedescribed below.

The light source 10B according to the second embodiment is a lightsource in conformity with a display for displaying an image such as aliquid crystal display backlight or the like. As shown in FIG. 58, thelight source 10B has a light emission section 14B comprising a matrix orstaggered pattern of electron emitters 12B corresponding to respectivelight-emitting devices such as pixels, and a drive circuit 16B fordriving the light emission section 14B. One electron emitter 12B may beassigned to each pixel, or a plurality of electron emitters 12B may beassigned to each pixel. In the present embodiment, it is assumed for thesake of brevity that one electron emitter 12B is assigned to each pixel.

The drive circuit 16B has a plurality of row select lines 144 forselecting rows in the light emission section 14B and a plurality ofsignal lines 146 for supplying data signals Sd to the light emissionsection 14B.

The drive circuit 16B also has a row selecting circuit 148 for supplyinga selection signal Ss selectively to the row select lines 144 tosuccessively select a row of electron emitters 12B, a signal supplyingcircuit 150 for supplying parallel data signals Sd to the signal lines146 to supply the data signals Sd to a row (selected row) selected bythe row selecting circuit 148, and a signal control circuit 152 forcontrolling the row selecting circuit 148 and the signal supplyingcircuit 150 based on a control signal (video signal or the like) Sv anda synchronizing signal Sc that are input to the signal control circuit152.

A power supply circuit 154 (which supplies 50 V and 0 V, for example) isconnected to the row selecting circuit 148 and the signal supplyingcircuit 150. A pulse power supply 156 is connected between a negativeline between the row selecting circuit 148 and the power supply circuit154, and GND (ground). The pulse power supply 156 outputs a pulsedvoltage waveform having a reference voltage (e.g., 0 V) during a chargeaccumulation period Td, to be described later, and a certain voltage(e.g., −400 V) during a light emission period Th.

During the charge accumulation period Td, the row selecting circuit 148outputs the selection signal Ss to the selected row and outputs anon-selection signal Sn to the unselected rows. During the lightemission period Th, the row selecting circuit 148 outputs a constantvoltage (e.g., −350 V) which is the sum of a power supply voltage (e.g.,50 V) from the power supply circuit 154 and a voltage (e.g., −400 V)from the pulse power supply 156.

The signal supplying circuit 150 has a pulse generating circuit 158 andan amplitude modulating circuit 160. The pulse generating circuit 158generates and outputs a pulse signal Sp having a constant pulse periodand a constant amplitude (e.g., 50 V) during the charge accumulationperiod Td, and outputs a reference voltage (e.g., 0 V) during the lightemission period Th.

During the charge accumulation period Td, the amplitude modulatingcircuit 160 amplitude-modulates the pulse signal Sp from the pulsegenerating circuit 158 depending on the luminance levels of thelight-emitting devices of the selected row, and outputs theamplitude-modulated pulse signal Sp as the data signal Sd for thelight-emitting devices of the selected row. During the light emissionperiod Th, the amplitude modulating circuit 160 outputs the referencevoltage from the pulse generating circuit 158 as it is. The timingcontrol in the amplitude modulating circuit 160 and the supply of theluminance levels of the selected light-emitting devices to the amplitudemodulating circuit 160 are performed through the signal supplyingcircuit 150.

For example, as indicated by three examples shown in FIGS. 50A through59C, if the luminance level is low, then the amplitude of the pulsesignal Sp is set to a low level Vsl (see FIG. 59A), if the luminancelevel is medium, then the amplitude of the pulse signal Sp is set to amedium level Vsm (see FIG. 59B), and if the luminance level is high,then the amplitude of the pulse signal Sp is set to a high level Vsh(see FIG. 59C). Though the amplitude of the pulse signal Sp is modulatedinto three levels in the above examples, if the amplitude modulation isapplied to the light source 10B, then the pulse signal Sp isamplitude-modulated to 128 levels or 256 levels depending on theluminance levels of the light-emitting devices.

A modification of the signal supplying circuit 150 will be describedbelow with reference to FIGS. 60 through 61C.

As shown in FIG. 60, a modified signal supplying circuit 150 a has apulse generating circuit 162 and a pulse width modulating circuit 164.The pulse generating circuit 162 generates and outputs a pulse signalSpa (indicated by the broken lines in FIGS. 61A through 61C) where thepositive-going edge of a voltage waveform (indicated by the solid linesin FIGS. 61A through 61C) applied to the electron emitter 12B iscontinuously changed in level, during the charge accumulation period Td.The pulse generating circuit 162 outputs a reference voltage during thelight emission period Th. During the charge accumulation period Td, thepulse width modulating circuit 164 modulates the pulse width Wp (seeFIGS. 61A through 61C) of the pulse signal Spa from the pulse generatingcircuit 162 depending on the luminance levels of the light-emittingdevices of the selected row, and outputs the pulse signal Spa with themodulated pulse width Wp as the data signal Sd for the light-emittingdevices of the selected row. During the light emission period Th, thepulse width modulating circuit 164 outputs the reference voltage fromthe pulse generating circuit 162 as it is. The timing control in thepulse width modulating circuit 164 and the supply of the luminancelevels of the selected pixels to the pulse width modulating circuit 164are also performed through the signal supplying circuit 150 a.

For example, as indicated by three examples shown in FIGS. 61A through61C, if the luminance level is low, then the pulse width Wp of the pulsesignal Spa is set to a short width, setting the substantial amplitude toa low level Vsl (see FIG. 61A), if the luminance level is medium, thenthe pulse width Wp of the pulse signal Spa is set to a medium width,setting the substantial amplitude to a medium level Vsm (see FIG. 61B),and if the luminance level is high, then the pulse width Wp of the pulsesignal Spa is set to a long width, setting the substantial amplitude toa high level Vsh (see FIG. 61C). Though the pulse width Wp of the pulsesignal Spa is modulated into three levels in the above examples, if theamplitude modulation is applied to the light source 10B, then the pulsesignal Spa is pulse-width-modulated to 128 levels or 256 levelsdepending on the luminance levels of the light-emitting devices.

Changes of the characteristics at the time the level of the negativevoltage for the accumulation of electrons will be reviewed in relationto the three examples of amplitude modulation on the pulse signal Spshown in FIGS. 59A through 59C and the three examples of pulse widthmodulation on the pulse signal Spa shown in FIGS. 61A through 61C. Atthe level Vsl of the negative voltage shown in FIGS. 59A and 61A, theamount of electrons accumulated in the electron emitter 12B is small asshown in FIG. 62A. At the level Vsm of the negative voltage shown inFIGS. 59B and 61B, the amount of electrons accumulated in the electronemitter 12B is medium as shown in FIG. 62B. At the level Vsh of thenegative voltage shown in FIGS. 59C and 61C, the amount of electronsaccumulated in the electron emitter 12B is large and is substantiallysaturated as shown in FIG. 62C.

However, as shown in FIGS. 62A through 62C, the voltage level at thepoint p4 where electrons start being emitted is substantially the same.That is, even if the applied voltage changes to the voltage levelindicated at the point p4 after electrons are accumulated, the amount ofaccumulated electrons does not change essentially. It can thus be seenthat a memory effect has been caused.

For using the electron emitter 12B as light-emitting device of the lightsource 10B, as shown in FIG. 63, a transparent plate 166 made of glassor acrylic resin is placed above the upper electrode 18, and a collectorelectrode 168 in the form of a transparent electrode, for example, isplaced on the reverse side of the transparent plate 166 (which faces theupper electrode 18), the collector electrode 168 being coated with aphosphor 170. A bias voltage source 172 (collector voltage Vc) isconnected to the collector electrode 168 through a resistor. Theelectron emitter 12B is naturally placed in a vacuum. The vacuum levelin the atmosphere should preferably in the range from 10² to 10⁻⁶ Pa andmore preferably in the range from 10⁻³ to 10⁻⁵ Pa.

The reason for the above range is that in a lower vacuum, (1) many gasmolecules would be present in the space, and a plasma can easily begenerated and, if too an intensive plasma were generated, many positiveions thereof would impinge upon the upper electrode 18 and damage thesame, and (2) emitted electrons would tend to impinge upon gas moleculesprior to arrival at the collector electrode 168, failing to sufficientlyexcite the phosphor 170 with electrons that are sufficiently acceleratedunder the collector voltage Vc.

In a higher vacuum, though electrons would be liable to be emitted froma point where electric field concentrates, structural body supports andvacuum seals would be large in size, posing disadvantages on efforts tomake the emitter smaller in size.

In the embodiment shown in FIG. 63, the collector electrode 168 isformed on the reverse side of the transparent plate 166, and thephosphor 170 is formed on the surface of the collector electrode 168(which faces the upper electrode 18). According to another arrangement,as shown in FIG. 64, the phosphor 170 may be formed on the reverse sideof the transparent plate 166, and the collector electrode 168 may beformed in covering relation to the phosphor 170.

Such another arrangement is for use in a CRT or the like where thecollector electrode 168 functions as a metal back. Electrons emittedfrom the emitter 22 pass through the collector electrode 168 into thephosphor 170, exciting the phosphor 170. Therefore, the collectorelectrode 168 is of a thickness which allows electrons to passtherethrough, preferably be 100 nm or less thick. As the kinetic energyof the emitted electrons is larger, the thickness of the collectorelectrode 168 may be increased.

This arrangement offers the following advantages:

(a) If the phosphor 170 is not electrically conductive, then thephosphor 170 is prevented from being charged (negatively), and anelectric field for accelerating electrons can be maintained.

(b) The collector electrode 168 reflects light emitted from the phosphor170, and discharges the light emitted from the phosphor 170 efficientlytoward the transparent plate 166 (light emission surface).

(c) Electrons are prevented from impinging excessively upon the phosphor170, thus preventing the phosphor 170 from being deteriorated and fromproducing a gas.

Four experimental examples (first through fourth experimental examples)of the electron emitter 12B used in the light source 10B according tothe second embodiment will be shown.

According to the first experimental example, the emission of electronsfrom the electron emitter 12B was observed. Specifically, as shown inFIG. 65A, a write pulse Pw having a voltage of −70 V was applied to theelectron emitter 12B to cause the electron emitter 12B to accumulateelectrons, and thereafter a turn-on pulse Ph having a voltage of 280 Vwas applied to cause the electron emitter 12B to emit electrons. Theemission of electrons was measured by detecting the light emission fromthe phosphor 170 with a light-detecting device (photodiode). Thedetected waveform is shown in FIG. 65B. The write pulse Pw and theturn-on pulse Ph had a duty cycle of 50%.

It can be seen from the first experimental example that light starts tobe emitted on a positive-going edge of the turn-on pulse Ph and thelight emission is finished in an initial stage of the turn-on pulse Ph.Therefore, it is considered that the light emission will not be affectedby shortening the period of the turn-on pulse Ph. This period shorteningwill lead to a reduction in the period to which the high voltage isapplied, resulting in a reduction in power consumption.

According to the second experimental example, how the amount ofelectrons emitted from the electron emitter 12B is changed by theamplitude of the write pulse Pw shown in FIG. 66 was observed. Changesin the amount of emitted electrons were measured by detecting the lightemission from the phosphor 170 with a light-detecting device(photodiode), as with the first experimental example. The experimentalresults are shown in FIG. 67.

In FIG. 67, the solid-line curve A represents the characteristics at thetime the turn-on pulse Ph had an amplitude of 200 V and the write pulsePw had an amplitude changing from −10 V to −80 V, and the solid-linecurve B represents the characteristics at the time the turn-on pulse Phhad an amplitude of 350 V and the write pulse Pw had an amplitudechanging from −10 V to −80 V.

As illustrated in FIG. 67, when the write pulse Pw is changed from −20 Vto −40 V, it can be understood that the light emission luminance changessubstantially straightly. A comparison between the amplitudes 350 V and200 V of the turn-on pulse Ph in particular indicates that a change inthe light emission luminance in response to the write pulse Pw at thetime the amplitude of the turn-on pulse Ph is 350 V has a wider dynamicrange, which is advantageous for increased luminance. If the lightsource 10B according to the second embodiment is applied to a display,then the contrast of the display can be increased. This tendency appearsto be more advantageous as the amplitude of the turn-on pulse Phincreases in a range until the light emission luminance is saturatedwith respect to the setting of the amplitude of the turn-on pulse Ph. Itis preferable to set the amplitude of the turn-on pulse Ph to an optimumvalue in relation to the withstand voltage and power consumption of thesignal transmission system.

According to the third experimental example, how the amount of electronsemitted from the electron emitter 12B is changed by the amplitude of theturn-on pulse Ph shown in FIG. 66 was observed. Changes in the amount ofemitted electrons were measured by detecting the light emission from thephosphor 170 with a light-detecting device (photodiode), as with thefirst experimental example. The experimental results are shown in FIG.68.

In FIG. 68, the solid-line curve C represents the characteristics at thetime the write pulse Pw had an amplitude of −40 V and the turn-on pulsePh had an amplitude changing from 50 V to 400 V, and the solid-linecurve D represents the characteristics at the time the write pulse Pwhad an amplitude of −70 V and the turn-on pulse Ph had an amplitudechanging from 50 V to 400 V.

As illustrated in FIG. 68, when the turn-on pulse Ph is changed from 100V to 300 V, it can be understood that the light emission luminancechanges substantially straightly. A comparison between the amplitudes 40V and −70 V of the write pulse Pw in particular indicates that a changein the light emission luminance in response to the turn-on pulse Ph atthe time the amplitude of the write pulse Pw is −70 V has a widerdynamic range, which is advantageous for increased luminance and alsoincreased contrast if the light source 10B is applied to a display. Thistendency appears to be more advantageous as the amplitude (in this case,the absolute value) of the write pulse Pw increases in a range until thelight emission luminance is saturated with respect to the setting of theamplitude of the write pulse Pw. It is preferable also in this case toset the amplitude (absolute value) of the write pulse Pw to an optimumvalue in relation to the withstand voltage and power consumption of thesignal transmission system.

According to the fourth experimental example, how the amount ofelectrons emitted from the electron emitter 12B is changed by the levelof the collector voltage Vc shown in FIG. 63 or 64 was observed. Changesin the amount of emitted electrons were measured by detecting the lightemission from the phosphor 170 with a light-detecting device(photodiode), as with the first experimental example. The experimentalresults are shown in FIG. 69.

In FIG. 69, the solid-line curve E represents the characteristics at thetime the level of the collector voltage Vc was 3 kV and the amplitude ofthe turn-on pulse Ph was changed from 80 V to 500 V, and the solid-linecurve F represents the characteristics at the time the level of thecollector voltage Vc was 7 kV and the amplitude of the turn-on pulse Phwas changed from 80 V to 500 V.

As illustrated in FIG. 69, it can be understood that a change in thelight emission luminance in response to the turn-on pulse Ph has a widerdynamic range when the collector voltage Vc is 7 kV than when thecollector voltage Vc is 3 kV, which is advantageous for increasedluminance and also increased contrast if the light source 10B is appliedto a display. This tendency appears to be more advantageous as the levelof the collector voltage Vc increases. It is preferable also in thiscase to set the level of the collector voltage Vc to an optimum value inrelation to the withstand voltage and power consumption of the signaltransmission system.

A drive method for the light source 10B according to the secondembodiment will be described below with reference to FIGS. 70 and 71.FIG. 70 shows operation of pixels in the first row and the first column,the second row and the first column, and the nth row and the firstcolumn. An electron emitter 12A used in the drive method has suchcharacteristics that the coercive voltage v1 at the point p2 shown inFIG. 55 is −20 V, for example, the coercive voltage v2 at the point p5is +70 V, the voltage v3 at the point p3 is −50 V, and the voltage v4 atthe point p4 is +50 V.

As shown in FIG. 70, if the period in which to select all the rows isdefined as one frame, then one charge accumulation period Td and onelight emission period Th are included in one frame, and n selectionperiods Ts are included in one charge accumulation period Td. Since eachselection period Ts becomes a selection period Ts for a correspondingrow, it becomes a non-selection period Tn for non-corresponding n-1rows.

According to the drive method, all the electron emitters 12B are scannedin the charge accumulation period Td, and voltages depending on theluminance levels of corresponding pixels to be turned on (to emit light)are applied to a plurality of electron emitters 12B which correspond tolight-emitting devices to be turned on, thereby accumulating charges(electrons) in amounts depending on the luminance levels of thecorresponding light-emitting devices in the electron emitters 12B whichcorrespond to the light-emitting devices to be turned on. In the nextlight emission period Th, a constant voltage is applied to all theelectron emitters 12B to cause the electron emitters 12B whichcorrespond to the light-emitting devices to be turned on to emitelectrons in amounts depending on the luminance levels of thecorresponding light-emitting devices, thereby emitting light from thelight-emitting devices to be turned on.

More specifically, as also shown in FIG. 71, in the selection period Tsfor the first row, a selection signal Ss of 50 V, for example, issupplied to the row selection line 144 of the first row, and anon-selection signal Sn of 0 V, for example, is applied to the rowselection lines 144 of the other rows. A data signal Sd supplied to thesignal lines 146 of the light-emitting devices to be turned on (to emitlight) of all the pixels of the first row has a voltage in the rangefrom 0 V to 30 V, depending on the luminance levels of the correspondinglight-emitting devices. If the luminance level is maximum, then thevoltage of the data signal Sd is 0 V. The data signal Sd is modulateddepending on the luminance level by the amplitude modulating circuit 160shown in FIG. 58 or the pulse width modulating circuit 164 shown in FIG.60.

Thus, a voltage ranging from −50 V to −20 V depending on the luminancelevel is applied between the upper and lower electrodes 18, 20 of theelectron emitter 12B which corresponds to each of the light-emittingdevices to be turned on in the first row. As a result, each electronemitter 12B accumulates electrons depending on the applied voltage. Forexample, the electron emitter 12B corresponding to the light-emittingdevice in the first row and the first column is in a state at the pointp3 shown in FIG. 55 as the luminance level of the pixel is maximum, andthe portion of the emitter 22 which is exposed through the throughregion 102 of the upper electrode 18 accumulates a maximum amount ofelectrons.

A data signal Sd supplied to the electron emitters 12B which correspondto light-emitting devices to be turned off (to extinguish light) has avoltage of 50 V, for example. Therefore, a voltage of 0 V is applied tothe electron emitters 12B which correspond to light-emitting devices tobe turned off, bringing those electron emitters 12B into a state at thepoint p1 shown in FIG. 55, so that no electrons are accumulated in thoseelectron emitters 12B.

After the supply of the data signal Sd to the first row is finished, inthe selection period Ts for the second row, a selection signal Ss of 50V is supplied to the row selection line 144 of the second row, and anon-selection signal Sn of 0 V is applied to the row selection lines 144of the other rows. In this case, a voltage ranging from −50 V to −20 Vdepending on the luminance level is also applied between the upper andlower electrodes 18, 20 of the electron emitter 12B which corresponds toeach of the light-emitting devices to be turned on. At this time, avoltage ranging from 0 V to 50 V is applied between the upper and lowerelectrodes 18, 20 of the electron emitter 12B which corresponds to eachof unselected light-emitting devices in the first row, for example.Since this voltage is of a level not reaching the point 4 in FIG. 55, noelectrons are emitted from the electron emitters 12B which correspond tothe light-emitting devices to be turned on in the first row. That is,the unselected light-emitting devices in the first row are not affectedby the data signal Sd that is supplied to the selected light-emittingdevices in the second row.

Similarly, in the selection period Ts for the nth row, a selectionsignal Ss of 50 V is supplied to the row selection line 144 of the nthrow, and a non-selection signal Sn of 0 V is applied to the rowselection lines 144 of the other rows. In this case, a voltage rangingfrom −50 V to −20 V depending on the luminance level is also appliedbetween the upper and lower electrodes 18, 20 of the electron emitter12B which corresponds to each of the light-emitting devices to be turnedon. At this time, a voltage ranging from 0 V to 50 V is applied betweenthe upper and lower electrodes 18, 20 of the electron emitter 12B whichcorresponds to each of unselected light-emitting devices in the firstthrough (n-1)th rows. However, no electrons are emitted from theelectron emitters 12B which correspond to the light-emitting devices tobe turned on, of those unselected light-emitting devices.

After elapse of the selection period Ts for the nth row, it is followedby the light emission period Th. In the light emission period Th, areference voltage (e.g., 0 V) is applied from the signal supplyingcircuit 150 to the upper electrodes 18 of all the electron emitters 12B,and a voltage of −350 V (the sum of the voltage of −400 V from the pulsepower supply 156 and the power supply voltage 50 V from the rowselecting circuit 148) is applied to the lower electrodes 20 of all theelectron emitters 12B. Thus, a high voltage (+350 V) is applied betweenthe upper and lower electrodes 18, 20 of all the electron emitters 12B.All the electron emitters 12B are now brought into a state at the pointp6 shown in FIG. 55. As shown in FIG. 57C, electrons are emitted fromthe portion of the emitter 22 where the electrons have been accumulated,through the through region 102. Electrons are also emitted from near theouter peripheral portion of the upper electrode 18.

Electrons are thus emitted from the electron emitters 12B whichcorrespond to the light-emitting devices to be turned on, and theemitted electrons are led to the collector electrodes 168 whichcorrespond to those electron emitters 12B, exciting the correspondingphosphors 170 which emit light. The emitted light is radiated outthrough the surface of the transparent plate 166.

Subsequently, electrons are accumulated in the electron emitters 12Bwhich correspond to the light-emitting devices to be turned on (to emitlight) in the charge accumulation period Td, and the accumulatedelectrons are emitted for fluorescent light emission in the lightemission period Th, for thereby radiating emitted light through thesurface of the transparent plate 166.

With the light source 10B according to the second embodiment, all theelectron emitters 12B are scanned in the charge accumulation period Tdin one frame, and voltages depending on the luminance levels ofcorresponding light-emitting devices are applied to electron emitters12B corresponding to the light-emitting devices to be turned on, therebyaccumulating amounts of charges depending on the luminance levels ofcorresponding light-emitting devices in the electron emitters 12Bcorresponding to the light-emitting devices to be turned on. In the nextlight emission period Th, a constant voltage is applied to all theelectron emitters 12B to cause a plurality of electron emitters 12Bwhich correspond to the light-emitting devices to be turned on to emitelectrons in amounts depending on the luminance levels of thecorresponding light-emitting devices, thereby emitting light from thelight-emitting devices to be turned on.

With the electron emitter 12B used in the light source 10B according tothe second embodiment, the voltage V3 at which the accumulation ofelectrons is saturated and the voltage V4 at which electrons start beingemitted satisfy the following relationship:1≦|V4|/|V3|≦1.5

Usually, if the electron emitters 12B are arranged in a matrix, and whena row of electron emitters 12B is selected at a time in synchronism witha horizontal scanning period and the selected electron emitters 12B aresupplied with a data signal Sd depending on the luminance levels of thelight-emitting devices, the data signal Sd is also supplied to theunselected light-emitting devices.

If the unselected electron emitters 12B emit electrons, for example, inresponse to the supplied data signal Sd, then the luminance of the lightsource 10B tends to suffer irregularities.

Since the electron emitter 12B has the above characteristics, however,even if a simple voltage relationship is employed such that the voltagelevel of the data signal Sd supplied to the selected electron emitters12B is set to an arbitrary level from the reference voltage to thevoltage V3, and a signal which is opposite in polarity to the datasignal Sd, for example, is supplied to the unselected electron emitters12B, the unselected light-emitting devices are not affected by the datasignal Sd supplied to the selected light-emitting devices. That is, theamount of electrons accumulated by each electron emitter 12B (the amountof charges in the emitter 22 of each electron emitter 12B) in theselection period Ts is maintained until electrons are emitted in thenext light emission period Th. As a result, each electron emitter 12Brealizes a memory effect for higher luminance and higher contrast.

With the light source 10B according to the second embodiment, necessarycharges are accumulated in all the electron emitters 12B in the chargeaccumulation period Td, and a voltage required to emit electrons isapplied to all the electron emitters 12B in the subsequent lightemission period Th to cause a plurality of electron emitters 12Bcorresponding to light-emitting devices to be turned on to emitelectrons thereby to emit light from the light-emitting devices to beturned on.

Usually, if light-emitting devices are constructed of the electronemitters 12B, then it is necessary to apply a high voltage to theelectron emitters 12B in order to emit light from the light-emittingdevices. For accumulating charges when the light-emitting devices arescanned and emitting light from the light-emitting devices, it isnecessary to apply a high voltage throughout a period (e.g., one frame)for emitting light from one light-emitting device, resulting in largeelectric power consumption. It is also necessary that the circuit forselecting the electron emitters 12B and supplying the data signal Sd bea circuit compatible with the high voltage.

In the present embodiment, after charges are accumulated in all theelectron emitters 12B, a voltage is applied to all the electron emitters12B to emit light from light-emitting devices corresponding to thoseelectron emitters 12B which are to be turned on.

Therefore, the period Th for applying the voltage (emission voltage) forelectron emission to all the electron emitters 12B is naturally shorterthan one frame. Furthermore, since the period for applying the emissionvoltage can be shortened as can be seen from the first experimentalexample shown in FIGS. 65A and 65B, the electric power consumption canbe much smaller than if charges are accumulated and light is emittedwhen the light-emitting devices are scanned.

Since the period Td in which charges are accumulated in the electronemitters 12B and the period Th in which electrons are emitted from theelectron emitters 12B corresponding to the light-emitting devices to beturned on are separate from each other, the circuit for applyingvoltages depending on luminance levels to the electron emitters 12B canbe driven at a lower voltage.

The data signal Sd and the selection signal Ss/non-selection signal Snin the charge accumulation period Td need to be applied to each row orcolumn. Since the drive voltage may be of several tens volts as can beseen in the above embodiments, an inexpensive multi-output driver foruse with fluorescent display tubes or the like can be used. In the lightemission period Th, the voltage for emitting sufficient electrons ispossibly higher than the drive voltage. However, because alllight-emitting devices to be turned on may be driven altogether,multi-output circuit components are not necessary. For example, a drivecircuit having one output and constructed of discrete components of ahigh withstand voltage is sufficient, the light source may beinexpensive and may be of a small circuit scale. The drive voltage anddischarge voltage may be lowered by reducing the film thickness of theemitter 22. The drive voltage may be set to several volts by setting thefilm thickness of the emitter 22.

According to the present drive method, furthermore, electrons areemitted in the second stage from all the light-emitting devices,independent of the row scanning, separately from the first stage basedon the row scanning. Consequently, the light emission time can easily bemaintained for increased luminance irrespective of the resolution andthe screen size.

Various modifications of the electron emitter 12B used in the lightsource 10B according to the second embodiment will be described belowwith reference to FIGS. 72 through 77.

As shown in FIG. 72, an electron emitter 12Ba according to a firstmodification has essentially the same structure as the electron emitter12B described above, and resides in that the upper electrode 18 is madeof the same material as the lower electrode 20, the upper electrode 18has a thickness t greater than 10 μm, and the through region 102 isartificially formed by etching (wet etching or dry etching), lift-off,and a laser beam. The through region 102 may be shaped as the hole 114,the recess 128, or the slit 132, as with the electron emitter 12Bdescribed above.

The peripheral portion 108 of the upper electrode 18 has a lower surface108 a slanted gradually upwardly toward the center of the peripheralportion 108 of the through region 102. The shape of the peripheralportion 108 can easily be formed by lift-off, for example.

The light source 10B which employs the electron emitter 12Ba accordingto the first modification, as with the electron emitter 12B describedabove, is capable of easily developing a high electric fieldconcentration, provides many electron emission regions, has a largeroutput and higher efficiency of the electron emission, and can be drivenat a lower voltage (lower power consumption).

FIG. 73 shows an electron emitter 12Bb according to a secondmodification. The electron emitter 12Bb has floating electrodes 174which are present on the portion of the upper surface of the emitter 22which corresponds to the through region 102.

FIG. 74 shows an electron emitter 12Bc according to a thirdmodification. The electron emitter 12Bc has upper electrodes 18 eachhaving a substantially T-shaped cross section.

FIG. 75 shows an electron emitter 12Bd according to a fourthmodification. The electron emitter 12Bd has an upper electrode 18including a lifted peripheral portion 108 of a through region 102. Toproduce such a shape, the film material of the upper electrode 18contains a material which will be gasified in the baking process. In theprocess, the material is gasified, forming a number of through regions102 in the upper electrode 18 and lifting the peripheral portions 108 ofthe through regions 102.

An electron emitter 12Be according to a fifth modification will bedescribed below with reference to FIG. 76.

As shown in FIG. 76, the electron emitter 12Be according to the fifthmodification has essentially the same structure as the electron emitter12B described above, but differs therefrom in that it has a singlesubstrate 176 of ceramics, a lower electrode 20 formed on the substrate176, an emitter 22 formed on the substrate 176 in covering relation tothe lower electrode 20, and an upper electrode 18 formed on the emitter22.

The substrate 176 has a cavity 178 defined therein at a position alignedwith the emitter 22 to form a thinned portion to be described below. Thecavity 178 communicates with the exterior through a through hole 180having a small diameter which is defined in the other end of thesubstrate 176 remote from the emitter 22.

The portion of the substrate 176 below which the cavity 178 is definedis thinned (hereinafter referred to as “thinned portion 182”). The otherportion of the substrate 176 is thicker and functions as a fixed section184 for supporting the thinned portion 182.

The substrate 176 comprises a laminated assembly of a substrate layer176A as a lowermost layer, a spacer layer 176B as an intermediate layer,and a thin layer 176C as an uppermost layer. The laminated assembly maybe regarded as an integral structure with the cavity 178 defined in theportion of the spacer layer 176B which is aligned with the emitter 22.The substrate layer 176A functions as a stiffening substrate and also asa wiring substrate. The substrate 176 may be formed by integrally bakingthe substrate layer 176A, the spacer layer 176B, and the thin layer176C, or may be formed by bonding the substrate layer 176A, the spacerlayer 176B, and the thin layer 176C together.

The thinned portion 182 should preferably be made of a highlyheat-resistant material. The reason for this is that if the thinnedportion 182 is directly supported by the fixed section 184 without usinga heat-resistant material such as an organic adhesive or the like, thethinned portion 182 is not be modified at least when the emitter 22 isformed.

The thinned portion 182 should preferably be made of an electricallyinsulating material in order to electrically isolate interconnectsconnected to the upper electrode 18 formed on the substrate 176 andinterconnects connected to the lower electrode 20 formed on thesubstrate 176.

The thinned portion 182 may thus be made of a material such as anenameled material where a highly heat-resistant metal or its surface iscovered with a ceramic material such as glass or the like. However,ceramics is optimum as the material of the thinned portion 182.

The ceramics of the thinned portion 182 may be stabilized zirconiumoxide, aluminum oxide, magnesium oxide, titanium oxide, spinel, mullite,aluminum nitride, silicon nitride, glass, or a mixture thereof. Of thesematerials, aluminum oxide and stabilized zirconium oxide areparticularly preferable because they provide high mechanical strengthand high rigidity. Stabilized zirconium oxide is particularly suitablebecause it has relatively high mechanical strength, relatively hightenacity, and causes a relatively small chemical reaction with the upperelectrode 18 and the lower electrode 20. Stabilized zirconium oxideincludes both stabilized zirconium oxide and partially stabilizedzirconium oxide. Stabilized zirconium oxide does not cause a phasetransition because it has a crystalline structure such as a cubicstructure or the like.

Zirconium oxide causes a phase transition between a monoclinic structureand a tetragonal structure at about 1000° C., and may crack upon such aphase transition. Stabilized zirconium oxide contains 1-30 mol % ofcalcium oxide, magnesium oxide, yttrium oxide, scandium oxide, ytterbiumoxide, cerium oxide, or an oxide of a rare earth metal. The stabilizershould preferably contain yttrium oxide for increasing the mechanicalstrength of the substrate 176. The stabilizer should preferably contain1.5 to 6 mol % of yttrium oxide, or more preferably 2 to 4 mol % ofyttrium oxide, and furthermore should preferably contain 0.1 to 5 mol %of aluminum oxide.

The crystalline phase of stabilized zirconium oxide may be a mixture ofcubic and monoclinic systems, a mixture of tetragonal and monoclinicsystems, or a mixture of cubic, tetragonal and monoclinic systems.Particularly, a mixture of cubic and monoclinic systems or a mixture oftetragonal and monoclinic systems is most preferable from the standpointof strength, tenacity, and durability.

If the substrate 176 is made of ceramics, then it is constructed ofrelatively many crystal grains. In order to increase the mechanicalstrength of the substrate 176, the average diameter of the crystalgrains should preferably be in the range from 0.05 to 2 μm and morepreferably in the range from 0.1 to 1 μm.

The fixed section 184 should preferably be made of ceramics. The fixedsection 184 may be made of ceramics which is the same as or differentfrom the ceramics of the thinned portion 182. As with the material ofthe thinned portion 182, the ceramics of the fixed section 184 may bestabilized zirconium oxide, aluminum oxide, magnesium oxide, titaniumoxide, spinel, mullite, aluminum nitride, silicon nitride, glass, or amixture thereof.

The substrate 176 used in the electron emitter 12Be is made of amaterial containing zirconium oxide as a chief component, a materialcontaining aluminum oxide as a chief component, or a material containinga mixture of zirconium oxide and aluminum oxide as a chief component.Particularly preferable is a material chiefly containing zirconiumoxide.

Clay or the like may be added as a sintering additive. Components ofsuch a sintering additive need to be adjusted so that the sinteringadditive does not contain excessive amounts of materials which caneasily be vitrified, e.g., silicon oxide, boron oxide, etc. This isbecause while these easily vitrifiable materials are advantageous injoining the substrate 176 to the emitter 22, they promote a reactionbetween the substrate 176 and the emitter 22, making it difficult tokeep the desired composition of the emitter 22 and resulting in areduction in the device characteristics.

Specifically, the easily vitrifiable materials such as silicon oxide inthe substrate 176 should preferably be limited to 3% by weight or lessor more preferably to 1% by weight or less. The chief component referredto above is a component which occurs at 50% by weight or more.

The thickness of the thinned portion 182 and the thickness of theemitter 22 should preferably be of substantially the same level. If thethickness of the thinned portion 182 were extremely larger than thethickness of the emitter 22 by at least ten times, then since thethinned portion 182 would work to prevent the emitter 22 from shrinkingwhen it is baked, large stresses would be developed in the interfacebetween the emitter 22 and the substrate 176, making the emitter 22 easyto peel off the substrate 176. If the thickness of the thinned portion182 is substantially the same as the thickness of the emitter 22, thesubstrate 176 (the thinned portion 182) is easy to follow the emitter 22as it shrinks when it is baked, allowing the substrate 176 and theemitter 22 to be appropriately combined with each other. Specifically,the thickness of the thinned portion 182 should preferably be in therange from 1 to 100 μm, more particularly in the range from 3 to 50 μm,and even more particularly in the range from 5 to 20 μm. The thicknessof the emitter 22 should preferably be in the range from 5 to 100 μm,more particularly in the range from 5 to 50 μm, and even moreparticularly in the range from 5 to 30 μm.

The emitter 22 may be formed on the substrate 176 by any of variousthick-film forming processes including screen printing, dipping,coating, electrophoresis, aerosol deposition, etc., or any of variousthin-film forming processes including an ion beam process, sputtering,vacuum evaporation, ion plating, chemical vapor deposition (CVD),plating, etc. Particularly, it is preferable to form a powderypiezoelectric/electrostrictive material as the emitter 22 and impregnatethe emitter 22 thus formed with glass of a low melting point or solparticles. According to this process, it is possible to form a film at alow temperature of 700° C. or lower or 600° C. or lower.

The material of the lower electrode 20, the material of the emitter 22,and the material of the upper electrode 18 may be successively bestacked on the substrate 176, and then baked into an integral structureas the electron emitter 12Be. Alternatively, each time the lowerelectrode 20, the emitter 22, or the upper electrode 18 is formed, theassembly may be heated (sintered) into an integral structure. Dependingon how the upper electrode 18 and the lower electrode 20 are formed,however, the heating (sintering) process for producing an integralstructure may not be required.

The sintering process for integrally combining the substrate 176, theemitter 22, the upper electrode 18, and the lower electrode 20 may becarried out at a temperature ranging from 500° to 1400° C., preferablyfrom 1000° to 1400° C. For heating the emitter 22 which is in the formof a film, the emitter 22 should preferably be sintered together withits evaporation source while their atmosphere is being controlled, sothat the composition of the emitter 22 will not become unstable at hightemperatures.

The emitter 22 may be covered with a suitable member, and then sinteredsuch that the surface of the emitter 22 will not be exposed directly tothe sintering atmosphere. In this case, the covering member shouldpreferably be of the same material as the substrate 176.

With the electron emitter 12Be according to the fifth modification, theemitter 22 shrinks when baked. However, stresses produced when theemitter 22 shrinks are released when the cavity 178 is deformed, theemitter 22 can sufficiently be densified. The densification of theemitter 22 increases the withstand voltage and allows the emitter 22 tocarry out the polarization inversion and the polarization changeefficiently, resulting in improved characteristics of the electronemitter 12Be.

According to the fifth modification, the substrate 176 comprises athree-layer substrate. FIG. 77 shows an electron emitter 12Bf accordingto a sixth modification which has a two-layer substrate 176 a which isfree of the lowermost substrate layer 176A.

As with the light source 10Ac according to the third modification shownin FIG. 16, the light source 10B according to the second embodiment mayhave its light emission section 14B divided into two groups (first andsecond groups G1, G2). When the electron emitters 12B in the group G1emit light, the electron emitters 12B in the group G2 may retrieveelectric power of the electron emitters 12B in the group G1, and whenthe electron emitters 12B in the group G2 emit light, the electronemitters 12B in the group G1 may retrieve electric power of the electronemitters 12A in the group G2.

As with the light source 10Ae according to the fifth modification shownin FIG. 29, the light source 10B according to the second embodiment mayhave two or more planar light source sections Z1 through Z6. In thefifth modification shown in FIG. 29, the light source 10Ae has sixplanar light source sections Z1 through Z6. Each of the planar lightsource sections Z1 through Z6 has a two-dimensional array of electronemitters 12B, and drive circuits 16B are independently connected to therespective planar light source sections Z1 through Z6.

Each of the planar light source sections Z1 through Z6 can be controlledfor energization/de-energization to perform stepwise light control(digital light control). Particularly, if the drive circuits 16Bindependently connected respectively to the planar light source sectionsZ1 through Z6 have modulation circuits 60 (see FIG. 18), then the lightemission distributions of the planar light source sections Z1 through Z6can independently be controlled. That is, the light source 10B canperform analog light control as well as digital light control for finelight control applications.

As with the light source 10Af according to the sixth modification shownin FIG. 30, the light source 10B according to the second embodiment mayinclude first and sixth planar light source sections Z1, Z6 which are ofa horizontally long rectangular shape with long sides, second and fifthplanar light source sections Z2, Z5 which are of a vertically longrectangular shape with long sides shorter than the long sides of thefirst and sixth planar light source sections Z1, Z6, and third andfourth planar light source sections Z3, Z4 which are of a horizontallylong rectangular shape with long sides shorter than the long sides ofthe first and sixth planar light source sections Z1, Z6.

As with the light source 10Ag according to the seventh modificationshown in FIG. 31, the light source 10B according to the secondembodiment may have first through sixth light source sections Z1 throughZ6, and the electron emitters 12A in each of the first through sixthlight source sections Z1 through Z6 may be divided into two groups(first and second groups G1, G2). In each of the first through sixthlight source sections Z1 through Z6, when the electron emitters 12B inthe group G1 emit light, the electron emitters 12B in the group G2 mayretrieve electric power of the electron emitters 12B in the group G1,and when the electron emitters 12B in the group G2 emit light, theelectron emitters 12B in the group G1 may retrieve electric power of theelectron emitters 12B in the group G2.

As with the light source 10Ah according to the eighth modification shownin FIG. 32, the light source 10B according to the second embodiment mayhave first through sixth light source sections Z1 through Z6, and thefirst through sixth light source sections Z1 through Z6 may be dividedinto two groups (first and second groups G1, G2). When the electronemitters 12B in the planar light source sections Z1 through Z3 in thegroup G1 emit light, the electron emitters 12B in the planar lightsource sections Z4 through Z6 in the group G2 may retrieve electricpower of the electron emitters 12B in the group G1, and when theelectron emitters 12B in the planar light source sections Z4 through Z6in the group G2 emit light, the electron emitters 12B in the planarlight source sections Z1 through Z3 in the group G1 may retrieveelectric power of the electron emitters 12B in the group G2.

The light source 10B according to the second embodiment may have thestructure of any of the light sources 10Ai through 10Am according to theninth through thirteenth modifications shown in FIGS. 33 through 37.

The light source 10A according to the first embodiment (includingvarious modifications) and the light source 10B according to the secondembodiment (including various modifications) offer the followingadvantages:

(1) Since the light source can produce higher luminance and consumelower electric power, it is optimum for use as projector light sourceswhich are required to have a luminance level of 2000 lumens.

(2) Because the light source can easily provide a high-luminancetwo-dimensional array light source, can be operated in a widetemperature range, and have their light emission efficiency unchanged inoutdoor environments, it is promising as an alternative of LEDs. Forexample, the light source is optimum as an alternative oftwo-dimensional array LED modules for traffic signal devices. At 25° C.or higher, LEDs have an allowable current lowered and produce lowluminance.

(3) Since a planar light source comprising a two-dimensional array ofelectron emitters can be turned on/off emitter by emitter, it ispreferable for use in applications where portions of a light emissionarea are turned on/off. Furthermore, because the planar light source caninstantaneously be turned on, it requires no time for warming up. If theplanar light source is used as the backlight of liquid crystal display,then the quality of moving images displayed thereby can be improved(moving image blurring can be improved) by high-speed blinking.

A preferred structure fabricated as a planar light source, i.e., a lightsource 10C according to a third embodiment, will be described below withreference to FIGS. 78 through 81.

As shown in FIG. 78, the light source 10C according to the thirdembodiment has a rear glass substrate 200 and a front glass substrate202 having a plate surface disposed in facing relation to a principalsurface of the rear glass substrate 200. The plate surface of the frontglass substrate 202 is coated with a white phosphor (not shown). Atwo-dimensional array of electron emitters 12B as shown in FIG. 38, forexample, is disposed on the principal surface of the rear glasssubstrate 200. A vacuum is developed between the rear glass substrate200 and the front glass substrate 202.

As shown in FIG. 79, the electron emitters 12B may comprise atwo-dimensional array of rectangular electron emission units 204(described later).

As shown in FIG. 80, each of the electron emission units 204 comprises asingle ferroelectric sheet 206 (emitter 22), a matrix of 16 upperelectrodes 18, for example, disposed on an upper surface of theferroelectric sheet 206, and a matrix of lower electrodes 20 (not shown)disposed on a lower surface of the ferroelectric sheet 206 at respectivepositions aligned with the upper electrodes 18. Specifically, each ofthe electron emission units 204 comprises a matrix of 16 electronemitters 12B.

In the arrangement shown in FIG. 80, in each of the electron emissionunits 204, the 16 upper electrodes 18 are arranged in four rows and fourcolumns. The four upper electrodes 18 in each row are electricallyconnected to each other by leads 208, and the four upper electrodes 18in the leftmost column are electrically connected to each other by leads210. The lower electrodes 20 are similarly arranged and electricallyconnected.

A plurality of lower electrode interconnects 212 are disposed on theprincipal surface of the rear glass substrate 200. A frame 214 ismounted on the principal surface of the rear glass substrate 200 wherethe lower electrode interconnects 212 are disposed. The frame 214 has aplurality of squares, arranged a matrix, for example, which are definedby a plurality of walls 216 arranged in rows and columns. The electronemission units 204 are inserted respectively in the squares. Each of thesquares as viewed in plan is slightly greater than a single electronemission unit 204, allowing the electron emission units 204 to be easilyinserted respectively in the squares. In FIGS. 79 and 80, some of theelectron emission units 204 are omitted from illustration for makingsome of the lower electrode interconnects 212 visible.

As shown in FIG. 80, upper electrode interconnects 218 are disposed onthe walls 216 of the frame 214. The lower electrode interconnects 212have a common lead 220, and the upper electrode interconnects 218 have acommon lead 222, the common leads 220, 222 extending to one side edge ofthe rear glass substrate 200.

The upper electrode interconnects 218 and the upper electrodes 18 of theelectron emission units 204 are electrically connected to each other byleads 224 extending from the upper electrodes 18 in the fourth columnsand electrically connected to the upper electrode interconnects 218disposed on the walls 216 near the upper electrodes 18 in the fourthcolumns, by an electrically conductive paste 226.

The lower electrode interconnects 212 and the lower electrodes 20 (notshown) are electrically connected to each other directly by anelectrically conductive paste (not shown) applied to the lower electrodeinterconnects 212 disposed on the principal surface of the rear glasssubstrate 200 and the lower electrodes 20.

The light source 10C according to the third embodiment operates asfollows: As shown in FIG. 78, electrons are emitted from the electronemitters 12B in each of the electron emission units 204 impinge upon thewhite phosphor (not shown) on the plate surface of the front glasssubstrate 202, exciting the white phosphor to emit fluorescent light.

If the light source 10C emits pulsed light at an emission frequency of300 Hz, then each of the emitted light pulses has a rise time ta of 1.7msec. from an emission start time t0 and a fall time tb of 3.3 msec.from the emission start time t0.

The light source 10C according to the third embodiment is capable ofemitting fluorescent light due to electron excitation in each of theelectron emission units 204 at an emission efficiency higher than theemission efficiency of LED light emission. The light source 10C is alsoadvantageous in that it has a reduced burden on the environment becauseit does not employ mercury.

The principles of the present invention may be applied to light sources,set forth below, other than the light sources, described above, foremitting light directly from a phosphor by having electrons emitted fromelectron emitters impinge upon the phosphor.

(1) Discharge lamps for utilizing emitted electrons to ignite or assistin an electric discharge, including discharge lamps for emitting visiblelight from a sealed gas rather than a phosphor.

(2) Light sources for emitting light from a phosphor that is excited byan ultraviolet radiation generated from a gas sealed in a space in thelight source, wherein the generation of the ultraviolet radiation isassisted by emitted electrons.

(3) Light sources for emitting light from a phosphor by having electronsand/or ions impinge upon the phosphor, the electrons and/or ions beingproduced when electrons impinge upon molecules of a gas sealed in aspace in the light source and ionize the molecules of the gas. In thiscase, emitted electrons impinging upon the gas molecules promote theionization thereof.

In any one of the applications (1), (2), and (3), the electron emittersmay be arranged in a two-dimensional array for producing an electricdischarge or generating an ultraviolet radiation or uniformizing theionization of gas molecules, thereby providing a planar light source foremitting uniform light.

FIG. 82 shows one such light source, i.e., a light source 10D accordingto a fourth embodiment of the present invention. The light source 10Daccording to the fourth embodiment has a rear glass substrate 200 and afront glass substrate 202 having a plate surface disposed in facingrelation to a principal surface of the rear glass substrate 200. Theplate surface of the front glass substrate 202 is coated with a phosphor(not shown). A two-dimensional array of electron emitters 12B as shownin FIG. 38, for example, is disposed on the principal surface of therear glass substrate 200. A space 230 defined between the rear glasssubstrate 200 and the front glass substrate 202, i.e., a space in thelight source, is filled with a gas 232. The gas 232 may be an Hg(mercury) gas or an Xe (xenon) gas.

Some of the electrons emitted from the electron emitters 12B impingeupon mercury particles in the gas 232, e.g., an Hg gas, exciting themercury particles to generate an ultraviolet radiation UV. Theultraviolet radiation UV hits the phosphor on the front glass substrate202, exciting the phosphor to emit fluorescent light 234.

A light source 10E according to a fifth embodiment of the presentinvention will be described below with reference to FIGS. 83 through 85.The principles of fluorescent light emission of the light source 10Eaccording to the fifth embodiment are identical to the principles offluorescent light emission of the light source 10D according to thefourth embodiment.

The light source 10E according to the fifth embodiment has a rear glasssubstrate 200 and a front glass substrate 202 having a plate surfacedisposed in facing relation to a principal surface of the rear glasssubstrate 200. The plate surface of the front glass substrate 202 iscoated with a white phosphor (not shown). A two-dimensional array ofelectron emitters 12B as shown in FIG. 38, for example, is disposed onthe principal surface of the rear glass substrate 200. The principalsurface of the rear glass substrate 200 is also coated with a whitephosphor 240. A space 230 defined between the rear glass substrate 200and the front glass substrate 202, i.e., a space in the light source, isfilled with a gas 232. The gas 232 may be an Hg (mercury) gas or an Xe(xenon) gas, as with the fourth embodiment.

The principal surface of the rear glass substrate 200 is divided into aplurality of first areas Za1 where electron emitters 12B are positioned,a plurality of second areas Za2 where the white phosphor 240 ispositioned, and a plurality of third areas Za3 where anode electrodes242, which are functionally equivalent to the collector electrode 32shown in FIG. 1, are positioned. The first areas Za1, the second areasZa2, and the third areas Za3 are arrayed in the order of a first areaZa1, a second area Za2, a third area Za3, a second area Za2, a firstarea Za1, . . . from the left, for example.

As shown in FIG. 85, each of the first areas Za1 has a lower electrodeinterconnect 212 and an upper electrode interconnect 218 that are spacedfrom, but disposed adjacent to, each other, and a plurality of electronemitters 12B spanning between the lower electrode interconnect 212 andthe upper electrode interconnect 218. Each of the electron emitters 12Bcomprises a ferroelectric chip 244 (emitter 22), an upper electrode 18disposed on an upper surface of the ferroelectric chip 244, and a lowerelectrode 20 (not shown) disposed on a lower surface of theferroelectric chip 244. The upper electrode 18 and the upper electrodeinterconnect 218 are electrically connected to each other by anelectrically conductive paste 246, and the lower electrode 20 and thelower electrode interconnect 212 are electrically connected to eachother by an electrically conductive paste 248. As shown in FIG. 84, thelower electrode interconnects 212 have a common lead 220 extending toone side edge of the rear glass substrate 200, and the upper electrodeinterconnects 218 have a common lead (not shown) extending to anotherside edge, e.g., a side edge opposite to the above one side edge, of therear glass substrate 200. The anode electrode 242 disposed in each ofthe third areas Za3 also extends to the other side edge of the rearglass substrate 200.

As shown in FIG. 83, electrons emitted from the electron emitters 12Barrayed in the first areas Za1 travel toward the anode electrodes 242disposed in the third areas Za3. Some of the electrons impinge upon gasparticles, e.g., mercury particles, of the gas 232, e.g., an Hg gas,exciting the gas particles to generate an ultraviolet radiation UV. Theultraviolet radiation UV hits the white phosphor 240 in the second areasZa2 and the white phosphor (not shown) on the front glass substrate 202,exciting these white phosphors to emit fluorescent light.

If the light source 10E emits pulsed light at an emission frequency of300 Hz, then each of the emitted light pulses has a rise time ta of 1.7msec. and a fall time tb of 3.3 msec. (see FIG. 81), as with the lightsource 10C according to the third embodiment.

The light source 10E according to the fifth embodiment can employ aphosphor for use in fluorescent lamps, and is capable of obtaining, inprinciple, the same light emission efficiency as with cold-cathodetubes.

The light source 10C according to the third embodiment and the lightsource 10E according to the fifth embodiment can be used as analternative to a cold-cathode tube, an LED, or a hot-cathode tube foruse as a back light source in a liquid crystal display panel, forexample.

Liquid crystal display panels for use on motor vehicles are required tohave a back light source that should be able to withstand a temperaturerange from −40 to +95° C. when in storage and a temperature range from−30 to +85° C. (at the panel) when in operation. The light source 10Caccording to the third embodiment and the light source 10E according tothe fifth embodiment (particularly if no mercury gas is employed) can beused in the above temperature ranges.

Although certain preferred embodiments of the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

1. A light source of a discharge lamp type, wherein electrons ignite orassist in an electric discharge; a source of said electrons comprises anelectron emitter; and said electron emitter comprises an emitter of adielectric material and a first electrode and a second electrode whichare disposed on said emitter; wherein when a drive voltage is appliedbetween said first electrode and said second electrode, at least aportion of said emitter has its polarization inverted or changed to emitelectrons.
 2. A light source according to claim 1, wherein when saiddrive voltage is applied between said first electrode and said secondelectrode, at least said portion of said emitter has its polarizationinverted to position positive poles of dipoles around said firstelectrode to draw primary electrons from said first electrode, and saidprimary electrons drawn from said first electrode impinge upon saidemitter to cause said emitter to emit secondary electrons.
 3. A lightsource according to claim 2, including: a triple point made up of saidfirst electrode, said emitter, and a vacuum atmosphere; wherein saidprimary electrons are drawn from a portion of said first electrode nearsaid triple point, and said primary electrons drawn from said firstelectrode impinge upon said emitter to cause said emitter to emitsecondary electrons.
 4. A light source according to claim 1, including:means for applying AC pulses between said first electrode and saidsecond electrode to cause at least said portion of said emitter to haveits polarization inverted or changed; wherein electrons areintermittently emitted from said emitter.
 5. A light source according toclaim 4, wherein before light emitted by a first emission of electronsis extinguished, next electrons are emitted to emit light continuously.6. A light source according to claim 1, including: a plurality of saidelectron emitters, said electron emitters being arranged in atwo-dimensional array.
 7. A light source according to claim 1,including: means for modulating said drive voltage based on a controlsignal to control an amount of electrons emitted from said electronemitter for controlling emitted light.
 8. A light source for emittinglight by exciting a phosphor with an ultraviolet radiation generatedfrom a gas sealed in a space in the light source, wherein electronsassist in generating the ultraviolet radiation from the gas; a source ofsaid electrons comprises an electron emitter; and said electron emittercomprises an emitter of a dielectric material and a first electrode anda second electrode which are disposed on said emitter; wherein when adrive voltage is applied between said first electrode and said secondelectrode, at least a portion of said emitter has its polarizationinverted or changed to emit electrons.
 9. A light source according toclaim 8, wherein when said drive voltage is applied between said firstelectrode and said second electrode, at least said portion of saidemitter has its polarization inverted to position positive poles ofdipoles around said first electrode to draw primary electrons from saidfirst electrode, and said primary electrons drawn from said firstelectrode impinge upon said emitter to cause said emitter to emitsecondary electrons.
 10. A light source according to claim 9, including:a triple point made up of said first electrode, said emitter, and avacuum atmosphere; wherein said primary electrons are drawn from aportion of said first electrode near said triple point, and said primaryelectrons drawn from said first electrode impinge upon said emitter tocause said emitter to emit secondary electrons.
 11. A light sourceaccording to claim 8, including: means for applying AC pulses betweensaid first electrode and said second electrode to cause at least saidportion of said emitter to have its polarization inverted or changed;wherein electrons are intermittently emitted from said emitter.
 12. Alight source according to claim 11, wherein before light emitted by afirst emission of electrons is extinguished, next electrons are emittedto emit light continuously.
 13. A light source according to claim 8,including: a plurality of said electron emitters, said electron emittersbeing arranged in a two-dimensional array.
 14. A light source accordingto claim 8, including: means for modulating said drive voltage based ona control signal to control an amount of electrons emitted from saidelectron emitter for controlling emitted light.
 15. A light source foremitting light from a phosphor by having electrons and/or ions impingeupon said phosphor, said electrons and/or ions being produced whenelectrons impinge upon molecules of a gas sealed in a space in saidlight source and ionize said molecules of the gas, wherein a source ofsaid electrons comprises an electron emitter; and said electron emittercomprises an emitter of a dielectric material and a first electrode anda second electrode which are disposed on said emitter; wherein when adrive voltage is applied between said first electrode and said secondelectrode, at least a portion of said emitter has its polarizationinverted or changed to emit electrons.
 16. A light source according toclaim 15, wherein when said drive voltage is applied between said firstelectrode and said second electrode, at least said portion of saidemitter has its polarization inverted to position positive poles ofdipoles around said first electrode to draw primary electrons from saidfirst electrode, and said primary electrons drawn from said firstelectrode impinge upon said emitter to cause said emitter to emitsecondary electrons.
 17. A light source according to claim 16,including: a triple point made up of said first electrode, said emitter,and a vacuum atmosphere; wherein said primary electrons are drawn from aportion of said first electrode near said triple point, and said primaryelectrons drawn from said first electrode impinge upon said emitter tocause said emitter to emit secondary electrons.
 18. A light sourceaccording to claim 15, including: means for applying AC pulses betweensaid first electrode and said second electrode to cause at least saidportion of said emitter to have its polarization inverted or changed;wherein electrons are intermittently emitted from said emitter.
 19. Alight source according to claim 18, wherein before light emitted by afirst emission of electrons is extinguished, next electrons are emittedto emit light continuously.
 20. A light source according to claim 15,including: a plurality of said electron emitters, said electron emittersbeing arranged in a two-dimensional array.
 21. A light source accordingto claim 15, including: means for modulating said drive voltage based ona control signal to control an amount of electrons emitted from saidelectron emitter for controlling emitted light.
 22. A light source of adischarge lamp type, wherein electrons ignite or assist in an electricdischarge; a source of said electrons comprises an electron emitter; andsaid electron emitter comprises an emitter of a dielectric material anda first electrode and a second electrode to which a drive voltage isapplicable to emit electrons from said emitter; said first electrodebeing disposed on a first surface of said emitter; said second electrodebeing disposed on a second surface of said emitter; at least said firstelectrode having a plurality of through regions through which saidemitter is exposed; and each of said through regions has a peripheralportion having a surface facing said emitter and spaced from saidemitter.
 23. A light source according to claim 22, wherein said firstelectrode emits electrons toward said emitter to charge said emitter ina first stage; and said emitter emits electrons in a second stage.
 24. Alight source according to claim 22, wherein electrons depending on anamount of charges on said emitter in a first stage are emitted from saidemitter in a second stage.
 25. A light source according to claim 22,wherein an amount of charges on said emitter in a first stage ismaintained until electrons are emitted from said emitter in a secondstage.
 26. A light source according to claim 22, wherein said emitter ismade of a piezoelectric material, an anti-ferroelectric material, or anelectrostrictive material.
 27. A light source according to claim 22,including: means for applying AC pulses between said first electrode andsaid second electrode to cause at least said portion of said emitter tohave its polarization inverted or changed; wherein electrons areintermittently emitted from said emitter.
 28. A light source accordingto claim 27, wherein before light emitted by a first emission ofelectrons is extinguished, next electrons are emitted to emit lightcontinuously.
 29. A light source according to claim 22, including: aplurality of said electron emitters, said electron emitters beingarranged in a two-dimensional array.
 30. A light source according toclaim 22, including: means for modulating said drive voltage based on acontrol signal to control an amount of electrons emitted from saidelectron emitter for controlling emitted light.
 31. A light source foremitting light by exciting a phosphor with an ultraviolet radiationgenerated from a gas sealed in a space in said light source, whereinelectrons assist in generating said ultraviolet radiation from said gas;a source of said electrons comprises an electron emitter; and saidelectron emitter comprises an emitter of a dielectric material and afirst electrode and a second electrode to which a drive voltage isapplicable to emit electrons from said emitter; said first electrodebeing disposed on a first surface of said emitter; said second electrodebeing disposed on a second surface of said emitter; at least said firstelectrode having a plurality of through regions through which saidemitter is exposed; and each of said through regions has a peripheralportion having a surface facing said emitter and spaced from saidemitter.
 32. A light source according to claim 31, wherein said firstelectrode emits electrons toward said emitter to charge said emitter ina first stage; and said emitter emits electrons in a second stage.
 33. Alight source according to claim 31, wherein electrons depending on anamount of charges on said emitter in a first stage are emitted from saidemitter in a second stage.
 34. A light source according to claim 31,wherein an amount of charges on said emitter in a first stage ismaintained until electrons are emitted from said emitter in a secondstage.
 35. A light source according to claim 31, wherein said emitter ismade of a piezoelectric material, an anti-ferroelectric material, or anelectrostrictive material.
 36. A light source according to claim 31,including: means for applying AC pulses between said first electrode andsaid second electrode to cause at least said portion of said emitter tohave its polarization inverted or changed; wherein electrons areintermittently emitted from said emitter.
 37. A light source accordingto claim 36, wherein before light emitted by a first emission ofelectrons is extinguished, next electrons are emitted to emit lightcontinuously.
 38. A light source according to claim 31, including: aplurality of said electron emitters, said electron emitters beingarranged in a two-dimensional array.
 39. A light source according toclaim 31, including: means for modulating said drive voltage based on acontrol signal to control an amount of electrons emitted from saidelectron emitter for controlling emitted light.
 40. A light source foremitting light from a phosphor by having electrons and/or ions impingeupon the phosphor, said electrons and/or ions being produced whenelectrons impinge upon molecules of a gas sealed in a space in saidlight source and ionize said molecules of the gas, wherein a source ofsaid electrons comprises an electron emitter; and said electron emittercomprises an emitter of a dielectric material and a first electrode anda second electrode to which a drive voltage is applicable to emitelectrons from said emitter; said first electrode being disposed on afirst surface of said emitter; said second electrode being disposed on asecond surface of said emitter; at least said first electrode having aplurality of through regions through which said emitter is exposed; andeach of said through regions has a peripheral portion having a surfacefacing said emitter and spaced from said emitter.
 41. A light sourceaccording to claim 40, wherein said first electrode emits electronstoward said emitter to charge said emitter in a first stage; and saidemitter emits electrons in a second stage.
 42. A light source accordingto claim 40, wherein electrons depending on an amount of charges on saidemitter in a first stage are emitted from said emitter in a secondstage.
 43. A light source according to claim 40, wherein an amount ofcharges on said emitter in a first stage is maintained until electronsare emitted from said emitter in a second stage.
 44. A light sourceaccording to claim 40, wherein said emitter is made of a piezoelectricmaterial, an anti-ferroelectric material, or an electrostrictivematerial.
 45. A light source according to claim 40, including: means forapplying AC pulses between said first electrode and said secondelectrode to cause at least the portion of said emitter to have itspolarization inverted or changed; wherein electrons are intermittentlyemitted from said emitter.
 46. A light source according to claim 45,wherein before light emitted by a first emission of electrons isextinguished, next electrons are emitted to emit light continuously. 47.A light source according to claim 40, including: a plurality of saidelectron emitters, said electron emitters being arranged in atwo-dimensional array.
 48. A light source according to claim 40,including: means for modulating said drive voltage based on a controlsignal to control an amount of electrons emitted from said electronemitter for controlling emitted light.